• Make the frosting first
• In the bowl of a stand mixer fitted with a paddle attachment, combine powdered sugar, salt, cream, and vanilla. Mix at low speed to moisten, then increase speed to medium and beat until creamy and soft, about 5 minutes. Using a spatula, scrape frosting into a small bowl, or as many bowls as you would like colors, and cover with plastic pressed directly against the surface. Set aside until needed, up to 24 hours at room temperature.

Make the Cookie Dough

• Preheat the oven to 350F. In the bowl of a standmixer fitted with a paddle attachment, combine butter, sugar, baking powder, and salt. Turn the mixer to the lowest speed for 1-2 minutes then turn the speed to medium for 3-4 minutes until the mixture is fluffy and pale.
• In a separate medium bowl, add the egg whites, cream, and vanilla. Mix with a fork or whisk to combine. Add the liquid mixture to the creamed butter and sugar in two parts, stopping the mixer to scrape bowl and beater about halfway through. Stop the mixer and add in the cake flour. Mix on low speed to combine, about 2 minutes.
• Scoop cookie dough into 2 tablespoon sized portions and place on a sheet tray lined with parchment paper, leaving at leave 3 inches between each cookie, they will spread. This will take multiple "rounds" or sheets to bake all of the dough.

  Bake at 350 for 11-14 minutes, the cookies should be puffed and pale, and just BARELY have some color around the edge.
• Add any food coloring you wish to the frosting and mix to combine until smooth. Decorate each cookie, one by one, by either dolloping the frosting onto the cooking and then spreading into an even layer with an offset spatula or by using a piping bag.

  Let the cookies stay uncovered at room temperature until frosting forms a crust. Enjoy! Store up to 3 days at room temperature in an airtight container.