Rainbow Cupcakes are a fun way to add color to your day! Soft vanilla cupcakes with layered batter and a swirl of vanilla buttercream make them perfect for birthday parties or a casual baking day.
Preheat the oven to 350 degrees Fahrenheit (175 degrees Celsius). Line one standard-size muffin tin with cupcake liners and set aside.
In the bowl of a stand mixer, cream the butter and sugar until light and fluffy, about 2 minutes. Add vanilla, then add eggs one at a time until incorporated.
In a small mixing bowl, whisk together the flour, baking powder, and salt. With the mixing speed on low, alternate adding the dry ingredients and wet ingredients (milk and sour cream). Mix until no flour pockets remain.
Remove the bowl from the stand and evenly divide the batter between six bowls. Color each bowl as desired (I used six colors: red, orange, yellow, green, blue, and purple), then place a layer of each into every cupcake liner. The batter should fill each about two-thirds of the way full.
Place in the oven and bake for 18–22 minutes or until the edges become lightly golden and the tops spring back. Be careful not to overbake! They will look slightly moist in the center. Remove from the oven and allow to cool in the pan for 3 minutes before transferring to a wire rack to cool completely.
For Vanilla Buttercream
In the bowl of a stand mixer fitted with the whisk attachment, beat the butter until smooth, about 1 minute. With mixing speed on low, add vanilla, salt, and powdered sugar. The mixture will look clumpy, and that’s okay. Add the heavy cream and gradually increase the mixing speed to high. Beat for 2–3 minutes or until the frosting is light and fluffy. Remove and pipe (or spread) onto cooled cupcakes. Top with desired sprinkles.
Notes
-A standard box cake mix can replace the vanilla cupcake recipe. It yields 24 cupcakes, so you’ll need to double the buttercream recipe.-I used six colors, but you can use as many as you like. Simply divide the batter evenly between however many bowls (colors) you want.STORE unfrosted cupcakes at room temperature in an airtight container for up to a week. Frosted cupcakes can be stored for up to 3 days this way. If FREEZING, wrap each unfrosted cupcake in plastic wrap and place them in an airtight container for up to 3 months.Let them thaw at room temperature before frosting and serving. To soften refrigerated cupcakes, let them sit at room temperature for about 30 minutes before serving.