Preheat oven to 375°F. Set aside an ungreased 10- inch tube pan. Place espresso in a cup, add boiling water and stir until smooth. Stir in vanilla and set aside.
Sift flour and 3/4 cup of the sugar onto a sheet of wax paper; sift again into a bowl and whisk together.
Using an electric mixer, beat egg whites at low speed for 1 minute. Beat in cream of tartar and salt, gradually increasing speed to medium, for 1 minute. Very slowly sprinkle in the remaining 3/4 cup sugar. Drizzle in cooled espresso and continue beating at medium speed until whites are stiff but not dry.
Sift about one-third of flour mixture on whites and fold in. Repeat folding in 2 more batches. Pour batter into pan. Bake until a tester comes out clean, 40 to 45 minutes.
Invert cake onto feet of pan (or place center tube over a bottle) to cool completely. Cut around center tube and side of pan with a thin, sharp knife, invert cake, and remove pan. Place cake right side up on a platter and drizzle Fudge Glaze over top.
Really good idea. It would get maximum stars from me, but I did have to make a couple changes, so I knocked it one. With a few tweaks, though, this is a wonderful, different take on a typical angel food. 1. I've never liked instant espresso when it can actually be tasted (in a chocolate recipe where it enhances flavor, more power to it), so I swapped the boiling water with 1/4 cup overly strong coffee. 2. The temp is way too high (unless my oven runs hot, which is possible), cooked too quickly on the outside and not quite enough inside. Next time I'll do it at 325-350. I will definitely make again. I didn't do a sauce, but there are a few recipes on here for them.