Step 1

Prepare for baking. Preheat the oven to 350°F / 180°C / gas mark Line aluminum baking sheets with parchment (baking) paper. Set aside.Sift dry ingredients. Sift the cake flour and baking powder into a medium bowl and whisk a few times.

Step 2

Combine wet ingredients. In a measuring cup or small bowl, whisk together the egg whites, cream, and vanilla extract until well combined and homogenous.

Step 3

Cream butter and sugar. In the mixing bowl of a stand mixer fitted with the paddle attachment, beat the butter and granulated sugar on medium speed until the mixture looks pale, creamy, and fluffy, for about 5 minutes.

Step 4

Make cookie dough. With the mixer running, add the egg white-cream mixture in 4 additions until combined. Scrape down the sides of the mixing bowl halfway through. Decrease the speed to low and add the cake flour mixture. Continue mixing until a soft dough forms and you no longer see streaks of flour.

Step 5

Scoop cookies. Use a 2-tablespoon cookie scoop to drop portions of dough onto the prepared baking sheets. Leave 3-in / 7 cm between each dough ball (the dough will spread as it bakes).

Step 6

Bake. Bake the cookies in the preheated oven for 12 to 15 minutes. The cookies should look puffy, pale, and barely golden around the edges.Cool. Let the cookies cool on the baking sheet for 15 minutes. Then place them in a single layer into an airtight container to cool completely. The container helps to seal in the moisture.

Step 7

Make frosting. Add the softened butter, powdered sugar, heavy cream, vanilla extract, and a few drops food coloring (if using) to the bowl of a stand mixer fitted with the whisk attachment (or to a large mixing bowl using a hand mixer). Start mixing on low speed to incorporate the powdered sugar. Then mix for 2 to 3 minutes on high speed until the frosting is light and fluffy.

Step 8

Frost cookies. Once cool, frost the cookies and decorate with sprinkles. The frosting sets quickly, so add sprinkles immediately after icing a cookie.

Step 9

Store. Store the cookies in a single layer in an airtight container. They will last for up to 5 days at room temperature.