Cream three-quarters cup of butter and one and one-quarter cups of sugar very well. Stop stirring, pour one-half cup of cold water on top of butter mixture and whites of eight eggs slightly beaten on top of water; do not stir, add one teaspoon of vanilla. Sift two and one-half cups of pastry flour, measure, then mix with two heaping teaspoons of baking-powder, and sift three times. Add to cake mixture and then beat hard until very smooth. Turn into ungreased angel cake pan, place in slow oven. Let cake rise to top of pan, then increase heat and bake until firm. Invert pan, when cool cut out.