1. Start oven, set at Moderately Slow, 275° F. Rub a cookie sheet with margarine or shortening, cover with waxed paper but do not grease the paper.
2. Mix and sift the flour and 1/4 cup of the sugar.
3. The egg whites with the salt until stiff; gradually beat in the remaining 1/2 cup sugar.
4. Sift the flour mixture over the beaten egg whites and fold it into them. Fold in the cooled, melted chocolate and the vanilla.
5. Drop from a teaspoon onto the prepared baking sheet. Bake 40 to 50 minutes.