I just made Box Cake Mix Cookie Bars that come out impossibly soft, ridiculously colorful, and gone before you can say party.
I’m obsessed with these Sugar Cookie Bars because they hit soft, chewy, stupidly fun vibes every time. I love how a box mix dessert recipes trick makes people think you slaved for hours.
The butter frosting is loud, sugary, and impossible to resist, and the way sprinkles peek through is basically shouting birthday. Quick Birthday Treats that actually taste like the real deal?
Yes. But mostly I adore the texture, tender edge, ultra-soft middle, and the nostalgia punch it delivers.
I grab white or funfetti cake mix and unsalted butter and they disappear faster than I can plate them now.
Ingredients
- Boxed cake mix gives sweetness and a quick base, makes life way easier.
- Melted butter adds richness and chew, makes edges slightly crisp.
- Soft butter makes silky frosting, easy to spread and taste indulgent.
- Eggs bind everything together, give structure and a tender crumb.
- Basically sour cream keeps bars chewy and adds subtle tang.
- Vanilla brings warm, familiar flavor; it’s tiny but essential.
- Powdered sugar sweetens frosting and gives that smooth, classic buttercream.
- Milk thins frosting to spreadable texture; you’ll add just enough.
- Plus vanilla in frosting rounds and deepens the sweetness.
- Rainbow sprinkles add playful color and a tiny sugary crunch.
Ingredient Quantities
- 1 box (15.25 oz) white or funfetti cake mix
- 1/2 cup (1 stick) unsalted butter, melted, plus 1/2 cup (1 stick) unsalted butter softened for frosting
- 2 large eggs
- 1/3 cup sour cream (for chewy texture)
- 1 teaspoon vanilla extract for the bars
- 3 cups powdered sugar for the buttercream
- 2 to 3 tablespoons milk (to thin the frosting as needed)
- 1 teaspoon vanilla extract for the frosting
- 2 to 3 tablespoons rainbow sprinkles, plus extra to decorate
How to Make this
1. Preheat oven to 350F and line a 9×13 inch pan with parchment or spray well with nonstick spray so the bars come out easy.
2. In a large bowl stir together 1 box (1
5.25 oz) white or funfetti cake mix, 1/2 cup melted unsalted butter, 2 large eggs, 1/3 cup sour cream, and 1 teaspoon vanilla extract until just combined and no big dry streaks remain, dont overmix or the bars will get cakey.
3. Press the dough evenly into the prepared pan using a spatula or your hands (you can wet your fingers a little so it doesnt stick) making a smooth layer.
4. Bake 18 to 22 minutes or until the edges are set and a toothpick in the center comes out with a few moist crumbs, not wet batter; cooking time varies by oven so check early to keep them soft and chewy.
5. Cool completely in the pan on a wire rack, at least 30 minutes, because warm bars will melt the frosting and sprinkles.
6. Meanwhile make the buttercream by beating 1/2 cup softened unsalted butter with 3 cups powdered sugar, 1 teaspoon vanilla extract, and 2 tablespoons milk; start slow so the sugar doesnt puff out, then beat until smooth and spreadable. Add another tablespoon milk if you need it thinner.
7. Fold 2 to 3 tablespoons rainbow sprinkles into the frosting gently if you want the confetti inside the frosting, but be warned they may bleed a bit into the icing color.
8. Spread the buttercream evenly over the cooled bars using an offset spatula or the back of a spoon, work quickly but gently so you dont tear the top.
9. Sprinkle extra rainbow sprinkles on top for decoration and press them in very lightly so they stick.
10. Chill the pan 15 to 20 minutes to set the frosting, then lift the parchment to remove the slab and cut into bars with a sharp knife, wiping the knife between cuts for clean edges. Store in an airtight container at room temp for 2 days or in the fridge for up to a week.
Equipment Needed
1. 9×13 inch baking pan (lined with parchment or well sprayed so bars come out easy)
2. Large mixing bowl
3. Hand mixer or whisk (hand mixer makes the buttercream way easier)
4. Rubber spatula or wooden spoon for stirring and pressing dough into the pan
5. Offset spatula or back of a spoon for spreading frosting
6. Measuring cups and spoons
7. Wire cooling rack
8. Sharp knife for cutting bars and a damp cloth to wipe between cuts
FAQ
Sugar Cookie Bars Recipe Substitutions and Variations
- Cake mix: Use 2 1/2 cups all purpose flour + 1 cup sugar + 1 tablespoon baking powder + 1/2 teaspoon salt and a few tablespoons of sprinkles if you want funfetti, mix dry then proceed like the box. It’s a bit more work but tastes fresher.
- Butter (melted or softened): Swap equal parts coconut oil or unsalted margarine, coconut gives a slight tropical note so reduce if you dont want that flavor, margarine works great for texture.
- Eggs: For 2 large eggs use 1/2 cup unsweetened applesauce (adds moisture, makes bars a touch denser) or 2 tablespoons ground flaxseed mixed with 6 tablespoons water, let sit 5 minutes till gelled, both are great egg-free options.
- Sour cream: Plain Greek yogurt is the best substitute, use same amount, gives the chewiness and tang without worrying about spoilage, or use buttermilk if thats what you have on hand.
Pro Tips
1) Don’t skip the sour cream. It’s the main reason these stay chewy. If you forget it the bars will be more cake like, so measure it out first and have it ready.
2) Press the dough evenly but don’t pack it too tight. Wet your fingers a tiny bit to smooth the top, it’ll stop the dough sticking and keeps the texture light. If you press too hard you’ll get dense bars.
3) Watch the oven closely starting at 16 minutes. Ovens vary a lot, and pulling them when there are just a few moist crumbs in the center keeps them soft. If you leave them in until completely dry they’ll be dry and crumbly.
4) Let the bars cool completely before frosting, and chill the frosted pan 15 to 20 minutes. Warm bars will melt the buttercream and the sprinkles will sink or bleed into the icing. If you need to speed things up, set the pan on a metal rack over a bowl of ice water for a few minutes, but don’t let them get cold spots.
Sugar Cookie Bars Recipe
I just made Box Cake Mix Cookie Bars that come out impossibly soft, ridiculously colorful, and gone before you can say party.
12
servings
507
kcal
Equipment: 1. 9×13 inch baking pan (lined with parchment or well sprayed so bars come out easy)
2. Large mixing bowl
3. Hand mixer or whisk (hand mixer makes the buttercream way easier)
4. Rubber spatula or wooden spoon for stirring and pressing dough into the pan
5. Offset spatula or back of a spoon for spreading frosting
6. Measuring cups and spoons
7. Wire cooling rack
8. Sharp knife for cutting bars and a damp cloth to wipe between cuts
Ingredients
-
1 box (15.25 oz) white or funfetti cake mix
-
1/2 cup (1 stick) unsalted butter, melted, plus 1/2 cup (1 stick) unsalted butter softened for frosting
-
2 large eggs
-
1/3 cup sour cream (for chewy texture)
-
1 teaspoon vanilla extract for the bars
-
3 cups powdered sugar for the buttercream
-
2 to 3 tablespoons milk (to thin the frosting as needed)
-
1 teaspoon vanilla extract for the frosting
-
2 to 3 tablespoons rainbow sprinkles, plus extra to decorate
Directions
- Preheat oven to 350F and line a 9×13 inch pan with parchment or spray well with nonstick spray so the bars come out easy.
- In a large bowl stir together 1 box (1
- 25 oz) white or funfetti cake mix, 1/2 cup melted unsalted butter, 2 large eggs, 1/3 cup sour cream, and 1 teaspoon vanilla extract until just combined and no big dry streaks remain, dont overmix or the bars will get cakey.
- Press the dough evenly into the prepared pan using a spatula or your hands (you can wet your fingers a little so it doesnt stick) making a smooth layer.
- Bake 18 to 22 minutes or until the edges are set and a toothpick in the center comes out with a few moist crumbs, not wet batter; cooking time varies by oven so check early to keep them soft and chewy.
- Cool completely in the pan on a wire rack, at least 30 minutes, because warm bars will melt the frosting and sprinkles.
- Meanwhile make the buttercream by beating 1/2 cup softened unsalted butter with 3 cups powdered sugar, 1 teaspoon vanilla extract, and 2 tablespoons milk; start slow so the sugar doesnt puff out, then beat until smooth and spreadable. Add another tablespoon milk if you need it thinner.
- Fold 2 to 3 tablespoons rainbow sprinkles into the frosting gently if you want the confetti inside the frosting, but be warned they may bleed a bit into the icing color.
- Spread the buttercream evenly over the cooled bars using an offset spatula or the back of a spoon, work quickly but gently so you dont tear the top.
- Sprinkle extra rainbow sprinkles on top for decoration and press them in very lightly so they stick.
- Chill the pan 15 to 20 minutes to set the frosting, then lift the parchment to remove the slab and cut into bars with a sharp knife, wiping the knife between cuts for clean edges. Store in an airtight container at room temp for 2 days or in the fridge for up to a week.
Notes
- Below you’ll find my best estimate of this recipe’s nutrition facts. Treat the numbers as a guide rather than a rule—great food should nourish both body and spirit. Figures are approximate, and the website owner assumes no liability for any inaccuracies in this recipe.
Nutrition Facts
- Serving Size: 104g
- Total number of serves: 12
- Calories: 507kcal
- Fat: 19.7g
- Saturated Fat: 11.2g
- Trans Fat: 0.43g
- Polyunsaturated: 1g
- Monounsaturated: 4.7g
- Cholesterol: 74mg
- Sodium: 160mg
- Potassium: 93mg
- Carbohydrates: 61g
- Fiber: 1.1g
- Sugar: 50.1g
- Protein: 3.5g
- Vitamin A: 167IU
- Vitamin C: 0mg
- Calcium: 56mg
- Iron: 1.2mg
