For the Almond Paste, grind the almonds through the finest blade of a food chopper. Then grind twice again. Mix in the powdered sugar. Blend in the egg whites and almond extract. Mold into a ball. Place in a tightly covered container and refrigerate for at least 4 days to age. Makes 1 pound. Preheat oven to 325 degrees. Soften the almond paste with your hands and work in the sugar, salt, flour, powdered sugar and egg whites. Drop by teaspoonfuls 5 cm apart onto ungreased wrapping paper placed on cookie sheets. Pat the tops lightly with fingers dipped in cold water. Bake for 18 to 20 minutes, or until set and delicately browned. Remove from the paper.