For White Cake

1. Preheat oven to 350F. Grease and flour three 8-inch round cake pans and place a small round of parchment paper in the bottom of each one. Set aside.
2. Add butter and sugar to a bowl and mix on medium-high speed until pale and fluffy, at least 5 minutes. Keep the mixer running on low and add egg whites one at a time until just combined.
3. Add vanilla and almond extracts and mix until combined. In a second bowl, stir together flour, baking powder, and salt.
4. Add the dry ingredients alternately with the milk in 2-3 additions, mixing on low until just combined. Divide batter between the pans evenly.
5. Bake cakes for about 25 minutes - watch carefully - until a cake tester or toothpick comes out with just a few moist crumbs.
6. Let cake layers cool in pan for 5 minutes, then invert onto cooling racks. Wait until they are fully cooled before frosting them.

For Boiled Frosting

1. Combine sugar, cream of tartar, and salt into a medium sauce pan. Stir, add water, and stir to combine.
2. Fit pot with candy thermometer. Bring mixture to a boil, stirring with a nonstick spatula, until it reaches the soft ball stage (240F). Remove from heat and allow to cool for a bit.
3. In a separate, large bowl, beat egg whites to soft peaks. Transfer sugar mixture to a container with a lip for easy pouring.
4. Stream sugar into egg whites while beating on medium high heat. When all of the syrup has been used, add almond extract and beat on high speed until stiff peaks are formed.

Assembly

1. If your cake layers have a significant dome, use a large serrated-edge knife to cut the layers flat.
2. On a cake plate, add one cake layer and top with frosting. Add second layer and top with more frosting. Add the last layer and top with frosting, then add frosting to the sides of the cake, filling in the gaps between the layers.