Instructions

1. Preheat oven to 350°F. 
2. Line a mini cupcake tray with mini cupcake liners. This can also be done with full-size cupcakes. (you’ll have more real-estate to write on them!)
3. Whisk the flour, cornstarch, baking powder, baking soda, and salt together. Set aside.
4. Using a handheld or stand mixer fitted with a paddle or whisk attachment, beat the butter on high speed until smooth and creamy, about 1 minute. Add the sugar and beat on high speed until creamed together, about 1 minute. Scrape down the sides and up the bottom of the bowl with a rubber spatula as needed. 
5. On high speed, beat in the egg whites until combined, then beat in the sour cream and vanilla extract.
6. Scrape down the sides and up the bottom of the bowl as needed. Pour the dry ingredients into the wet ingredients. Turn the mixer to low speed and as the mixer runs, slowly pour in the milk. Beat on low speed just until all of the ingredients are combined. Do not over-mix. You may need to whisk it all by hand to make sure there are no lumps at the bottom of the bowl. The batter will be slightly thick. Gently fold in the sprinkles.
7. Pour batter evenly into the prepared cupcake pan.
8. Bake for around 15-17 minutes or until the cake is baked through. To test the cake for doneness, insert a toothpick into the center of the cake. If it comes out clean, it’s done.
9. Allow the cupcakes to cool completely in the pan set on a wire rack. The cake must be completely cool before frosting.
10. Make the buttercream: With a handheld or stand mixer fitted with a paddle attachment, beat the butter on medium speed until creamy, about 1 minute. Add the confectioners’ sugar, heavy cream, and clear vanilla extract. Beat on low speed for 30 seconds, then increase to medium-high speed and beat for 2 full minutes. Add up to 1/4 cup (30g) more confectioners’ sugar if frosting is too thin or a splash of heavy cream if frosting is too thick. Add a pinch of salt if the frosting is too sweet.
11. Divide the buttercream up evenly into four bowls, and dye to your desired pastel shades.
12. Decorate: Once the mini cupcakes have cooled, use a ziploc or piping bag to frost each cupcake in the shape of a heart. Lay frosting-side down on a parchment-lined baking tray. Once they are all frosted, refrigerate until the frosting is firm and flat on top.
13. Melt white chocolate and dye with red food coloring. You can thin it out with a bit of vegetable oil if necessary. Then pipe the white chocolate onto the cupcakes, with whatever phrases you want (and can fit)