Birthday Cake Blondies Recipe

Updated March 19, 2024

These festive Birthday Cake Blondies blend the rich, buttery foundation of classic blondies with playful sprinkles, creating a treat that evokes the joy of a celebratory birthday cake. Soft, chewy, and vibrantly decorated, they’re perfect for parties, gatherings, or simply satisfying a sweet tooth.

Recipe Overview

  • Total Time: 35 minutes (plus cooling time)

  • Prep Time: 5 minutes

  • Cook Time: 30 minutes (25 minutes baking + 5 minutes cooling)

  • Difficulty: Easy

Ingredients

Yields: 16 small squares (8×8 inch pan) or similar

  • For greasing the pan: 1 tablespoon unsalted butter, softened

  • Dry ingredients:

  • 1 cup (130g) all-purpose flour

  • ½ teaspoon baking powder

  • ½ teaspoon fine sea salt

  • Wet ingredients:

  • 1 cup (189g) lightly packed light or dark brown sugar

  • ½ cup (113g) unsalted butter, softened to room temperature

  • 1 large egg (50–55g)

  • 1 teaspoon pure vanilla extract

  • Add-ins & decorations:

  • ¼ cup (40g) sprinkles (e.g., rainbow, matte, or seasonal shapes), plus extra for topping

Preparation Instructions

Step 1: Preheat Oven and Prep Pan

Preheat the oven to 350°F (175°C) and position the rack in the center. Lightly grease an 8-inch square baking pan with softened butter, ensuring all interior surfaces (sides and bottom) are coated to prevent sticking.

Step 2: Combine Dry Ingredients

In a small mixing bowl, whisk together the all-purpose flour, baking powder, and fine salt until thoroughly blended. This step ensures even distribution of leavening agents and prevents lumps in the batter.

Step 3: Cream Wet Ingredients

In a large mixing bowl, add the softened brown sugar and butter. Using a flexible spatula or an electric hand mixer (for efficiency), cream the butter and sugar together until smooth and pale in color, approximately 2–3 minutes. The mixture should lose its granular texture and become fluffy.

Add the large egg and vanilla extract, then continue mixing until fully incorporated. The batter will appear glossy and well-blended, about 1–2 minutes longer.

Step 4: Integrate Dry Ingredients and Add Sprinkles

Gradually pour the dry ingredient mixture into the wet ingredients. Using a gentle folding motion with the spatula, mix just until no dry flour streaks remain—do not overmix, as this can result in dense blondies.

Fold in ¼ cup sprinkles, stirring them evenly throughout the batter.

Step 5: Bake and Decorate

Transfer the batter to the prepared pan, spreading it with a spatula to create an even layer (approximately 1 inch deep). Generously sprinkle additional sprinkles on top for a festive, "birthday cake" appearance.

Step 6: Bake Until Golden

Place the pan on the center rack of the preheated oven and bake for 25–30 minutes. The edges should be golden brown, and the center will be set (it may jiggle slightly but should not be wet). Start checking at 25 minutes to avoid overbaking.

Step 7: Cool and Slice

Remove the pan from the oven and let the blondies cool completely in the pan on a wire rack for 15–20 minutes. This allows the structure to set, making slicing cleaner. Once cooled, cut into squares or rectangles.

Storage & Shelf Life

Store cooled blondies in an airtight container at room temperature for up to 3 days. For longer storage, wrap individual pieces in parchment paper and freeze for up to 3 months. Thaw at room temperature before serving to restore texture.

Tips & Variations

Sprinkle Selection

  • Shiny sprinkles: May slightly melt or bleed color on top but still add visual appeal.

  • Matte sprinkles: Retain their shape and color better in the oven, ideal for even distribution.

  • Customization: Swap sprinkles for chocolate chips, chopped nuts (pecans/walnuts), flaked coconut, or seasonal M&Ms for variation.

Reader-Tested Add-Ins

  • Snickerdoodle twist: Top with powdered sugar, cinnamon, and nutmeg after baking.

  • Sweet-salty balance: Sprinkle flaky sea salt on top before baking.

  • Rich mix-ins: Add 1 cup total of chocolate chips, nuts, and/or coconut for extra indulgence.

Reader Reviews

  • "The sprinkles are what make these 'birthday cake' blondies. Leave them out, and you’re just making regular blondies!"

  • "I added a pinch of flaky salt on top before baking—it took it to the next level. So good!"

  • "Used a hand mixer for the initial butter-sugar mixture, then a spatula for flour. Perfect texture at 25 minutes. Sprinkles look festive but don’t overpower flavor!"

  • "Super easy and perfect as-is! Made this dozens of times—never disappoints."

Enjoy these chewy, celebratory blondies at your next gathering or as a special treat! 🎂