1. Preheat oven to 325°.
2. Combine almond flour, 1/3 cup sugar, and cocoa in a medium bowl; stir well with a whisk.
3. Place egg whites in a large bowl; beat with a mixer at high speed until foamy. Add cream of tartar; beat until soft peaks form. Add 1/3 cup sugar, 1 tablespoon at a time, beating until stiff peaks form. Fold in almond extract. Sprinkle flour mixture over egg white mixture; fold in.
4. Spoon mixture into a pastry bag fitted with a 1/4-inch round tip. Pipe 53 (1 1/2-inch-round) mounds 1 inch apart onto baking sheets lined with parchment paper. Gently press an almond slice into top of each cookie. Bake at 325° for 12 to 15 minutes or until edges of cookies are crisp. Cool 10 minutes on pans. Remove cookies from pans; cool on wire racks.