Special equipment: an angel food or tube pan, preferably with cooling legs
For the angel food cake: Preheat the oven to 350 degrees F.
Combine the cake flour and salt in a medium bowl and sift together 5 times. Set aside.
In a large bowl, with an electric mixer fitted with the whisk attachment, beat the egg whites until frothy (lots of bubbles but still liquid and loose). Add the cream of tartar and beat on high until stiff, 4 to 5 minutes. With the mixer on medium low, slowly sprinkle in the sifted granulated sugar. Fold in the sifted flour mixture gently until it's all combined. Sprinkle the vanilla into the bowl and fold gently.
Spoon the batter into an angel food or tube pan (preferably with cooling legs)--make sure there's no grease or butter in there! Smooth the top and bake until a wooden skewer stuck all the way to the bottom comes out clean, 35 to 45 minutes. (Don't open the oven while it's baking!)
Carefully remove the cake from the oven and immediately invert it onto its cooling legs (see Cook's Note). Let the cake cool completely while upside-down.
For the frosting: Beat the powdered sugar, butter and cream in a large bowl with an electric mixer until very light and fluffy. Add a few drops of yellow food coloring as desired.
Carefully remove the cake from the pan and transfer it to a cake plate upside-down, so that the end that was stuck to the bottom of the pan is now facing up. Frost the cake all over.
If your pan doesn't have cooling legs, immediately invert the tube pan onto a vinegar or wine bottle for cooling. Let the cake cool completely while upside-down.