To make the cake
Preheat oven to 325°F. In a large bowl with an electric mixer, beat egg whites until frothy. Add cream of tartar, salt, lemon oil, and vanilla. Continue beating until whites form stiff but not dry peaks.

Using a rubber spatula, gradually fold in sugar, a few tablespoons at a time. Gradually fold in flour, one quarter at a time. Be sure you use a true folding motion, gently turning the spatula from the bottom of the bowl to the top, folding in air with each stroke, as opposed to beating or stirring. You just went to all that work whipping the egg whites, so you don’t want to beat them to death.

Pour batter into an ungreased 9-inch angel food cake pan. Bake for 1 hour, or until top is golden brown and cake pulls away from pan sides.

Remove cake from oven. Cool in pan for 10 minutes, then invert and cool on pan legs, or hang pan over the neck of a bottle, for 1 hour, or until cooled. Run a knife around sides and tube of cake and unmold cake.

To make the glaze
While cake is cooling, in a small bowl, whisk together confectioners’ sugar, lemon zest, and lemon juice. Let stand for 10 minutes before glazing the cake, since it will thicken a little. Using a toothpick, poke holes in top of cake, 1/2-inch apart, so that glaze can seep in. Pour glaze over cake. Serve.