Birthday Cake Cupcakes

Preheat the oven to 350℉ (177℃). Line cupcake pans with 14 cupcake liners.
In a small mixing bowl, whisk together the all-purpose flour, baking powder, and salt. Set aside.
In the bowl of a stand mixer fitted with a paddle attachment or in a large mixing bowl with an electric hand mixer, cream the granulated sugar, unsalted butter, and vegetable oil for a few minutes until light and creamy. Add the egg whites, sour cream, and vanilla extract and mix until smooth.
Add in half of the dry ingredients and mix until mostly combined. Then, pour in the milk and mix. Add the remaining dry ingredients and mix until the cupcake batter is combined and smooth. Scrape the sides and bottom of the bowl to ensure the ingredients are fully combined. Fold in the rainbow sprinkles.
Portion the cupcake batter into the cupcake liners using a large cookie scoop about ⅔ full. Bake the cupcakes for 20 minutes or until the cupcakes bounces back when gently touched. Cool the cupcakes in the pan for 2 minutes and then transfer to a wire rack to cool completely.

First, heat-treat the white cake mix. Pour the cake mix into a microwave-safe bowl. Heat the cake mix in the microwave for 30 seconds and then stir. Repeat this process until the cake mix reaches 160℉ (71℃), about 1-1½ minutes total. If the cake mix is lumpy, run it through a fine mesh strainer and then set aside to cool.
In the bowl of a stand mixer fitted with a paddle attachment or in a large mixing bowl with an electric hand mixer, whip the room temperature unsalted butter for 5 minutes until light, pale, and creamy.
Add in half of the powdered sugar and mix on the lowest speed until the sugar is combined with the butter. Add the remaining half of the powdered sugar and the cooled heat-treated white cake mix and continue to mix on low speed until fully combined.
Add in the heavy cream, vanilla extract, and salt, and continue to mix on low speed until combined and smooth. Scrape the sides and bottom of the bowl to ensure the ingredients are well incorporated.
Increase the mixer speed to medium and whip the buttercream for about 3 to 5 minutes until it is smooth and creamy. Then, turn the mixer to low speed and mix the buttercream for several minutes to remove air bubbles.
Optional: To smooth out the buttercream, melt 1 cup of the frosting in the microwave for 15 seconds. Pour the melted frosting back into the mixing bowl and mix the frosting on low speed until the buttercream is super smooth and creamy.

Preheat the oven to 350℉ (177℃). Line a baking sheet pan with parchment paper.
In a medium mixing bowl, whisk together the cake flour, granulated sugar, light brown sugar, baking powder, and salt until well combined. Add in the vegetable oil and vanilla extract and stir until the dry and wet ingredients are fully incorporated and large clusters form. Add in the rainbow nonpareil sprinkles and stir until they are well dispersed throughout the mixture. Break up any larger clusters with a spoon.
Spread the birthday cake crumb mixture onto the prepared baking sheet pan. Bake the crumbs for 10 minutes. After baking, cool the birthday cake crumbs to room temperature and then break them up into small crumbs.

Fill a piping bag fitted with a Wilton 1M piping tip with the cake batter buttercream frosting. Pipe a generous swirl of the frosting onto the cooled funfetti cupcakes. Pile the cupcakes high with the birthday cake crumbs and decorate with additional rainbow sprinkles.

Storing & Serving:

Room temperature: Store the cupcakes in an airtight container at room temperature for 2 to 3 days.
Refrigerator: Store the cupcakes in an airtight container in the refrigerator for 3 to 4 days. Serve at room temperature for the best taste and texture.

Note: Metric conversions and nutritional information are calculated automatically. I cannot guarantee the accuracy of this information.