Preheat oven to 275 degrees.
Sift flour once. Add cocoa and sift four more times.
Beat egg whites and salt; when foamy add cream of tartar and continue beating until eggs are stiff enough to hold up in peaks but not dry.
Carefully fold in sugar 2 tablespoons at a time until all is used.
Fold in vanilla.
Then sift small amount of flour over mixture and fold in carefully.
Continue until all is used.
Pour batter in to ungreased 10 inch angel food tube pan.
Bake at least 1 hour.
Begin at 275 degrees and after 30 minutes increase heat slightly to 325 degrees and bake 30 minutes longer.
Remove cake from oven and invert pan 1 hour or until cold.
Remove cake from pan.
Drizzle with warm butterscotch sauce.
To serve gently pull pieces of cake apart with two forks.
Never cut an angel food cake.

Melt butter with brown sugar in top of double boiler.
Add milk, salt, and soda.
Cook until hot.
May be kept in refrigerator several weeks.
Heat to serve.