Cupcakes

1. While the eggs are cold, separate and reserve the egg whites. Adjust the quantity of eggs slightly if needed to reach 3/4 C whites. It’s very important that the whites are completely free of yolk and shell, or they may not “fluff” when beating them later. Cover the egg whites and bring to room temperature (around 70 degrees F) for 1 1/2 to 2 hours.
2. While the egg temperature rises, measure the flour and powdered sugar, then sift them together with the salt. Measure cream of tartar, sugar, and vanilla each into separate bowls so they’re ready to add to the mixer while it’s running.
3. Have a nonstick cupcake pan ready (see notes).
4. When the eggs are ready, preheat the oven to 350 degrees (F), and add eggs to a completely clean metal or glass bowl of a stand mixer fitted with the whisk attachment. Whisk on medium low speed (4 of 10) until frothy, about 2 minutes. With the mixer running, add cream of tartar, increase speed 1 “notch” (6 of 10) and beat until soft peaks form, about 3 minutes. You should turn off the mixer to check this when the eggs look close, to make sure you don’t overbeat them into stiff peaks. After confirming, resume beating at medium low speed (a 4, again), adding a tablespoon of sugar about every 30 seconds. Beat another minute after adding the last of the sugar, then check for only slightly stiffer peaks. They should not be completely stiff. The process of adding sugar and beating for an additional minute took me 4 minutes. Egg temperature will impact mixing times, so watch for the signs indicated, even if it takes a minute or two longer to get there.
5. Gently drizzle vanilla over surface of the egg mixture and beat on low speed until just incorporated.
6. In four batches, sprinkle the dry ingredient mixture over the surface of the batter and use a rubber spatula to gently fold by hand until incorporated smoothly. Be patient with the folding–it’s necessary to keep the air pockets, the only leavening agent in angel food, in the batter.
7. Use a spring ice cream scoop or one third cup measure to evenly distribute all the batter amongst 12 cupcake wells. Bake for 18 to 20 minutes, until tops are golden and spring back slightly when touched. Don’t open the oven until you suspect the cakes are close to being done.
8. If using an unlined nonstick pan, cool the cupcakes upside down, with the pan carefully propped at each corner on a can or other level items. Remove cupcakes from pan once cooled. If not using liners, slide a small paring knife around the outside of each cupcake to loosen it. I also used a large spoon to sort of scoop the cupcake out of the well gently.
9. Once cooled completely, frost or wrap individually in plastic wrap (see notes).

Icing

1. Place white chocolate in a completely dry glass bowl set over a saucepan of water (water shouldn’t touch bottom of bowl). Heat over medium (to eventually simmer the water), stirring more frequently with a rubber or silicone heat-safe spatula as the chocolate begins to melt. When almost completely melted, remove bowl to a towel or potholder, careful not to get any water in the chocolate. Continue stirring until fully melted, then allow to cool while you start the icing.
2. In an electric mixer fitted with a paddle attachment, or in a bowl using a hand mixer, beat butter at medium high speed until lightened and creamy, a minute or two. Scrape down sides of bowl as needed. Beat in vanilla until incorporated.
3. Add powdered sugar a little at a time, reducing mixer speed to low when initially adding the sugar, so it doesn’t fly everywhere. Increase speed to fully incorporate, then repeat the process until all the sugar is added. Scrape down sides of bowl as needed.
4. With the mixer running on low speed, constantly drizzle in the melted, cooled white chocolate until fully incorporated. Don’t turn up the speed on the mixer; the goal is to stir in the chocolate. Add milk or cream and beat on low speed, to soften the frosting slightly. If you prefer a more liquid consistency, add more milk a teaspoon at a time.
5. Work with the frosting immediately, frosting the cupcakes by hand or using a bag and frosting/decorating tip as I did (you can see in the photo, my setup is nothing fancy–a heavy duty resealable plastic bag with icing tip inserted). Alternately, refrigerate icing in airtight container, then bring almost to room temperature before using, to soften the frosting.
6. Decorate cupcakes with sprinkles of your choice!