1. Preheat oven to 350°.
2. Weigh or lightly spoon flour into dry measuring cups; level with a knife. Combine flour, flaxseed, soda, and salt in a bowl, stirring with a whisk. Combine sugars, egg whites, and egg in a bowl; beat with a mixer at high speed for 2 minutes. Add vanilla; mix well. Add flour mixture to egg mixture; stir until combined. Fold in chocolate and almonds. Divide dough into 3 equal portions. Roll each portion into a 6-inch-long roll. Arrange rolls 3 inches apart on a baking sheet lined with parchment paper. Pat to a 1-inch thickness. Bake at 350° for 28 minutes or until firm.
3. Remove rolls from baking sheet; cool 10 minutes on a wire rack. Cut rolls diagonally into 30 (1/2-inch) slices. Place, cut sides down, on baking sheet. Reduce oven temperature to 325°; bake 7 minutes. Turn cookies over; bake 7 minutes (cookies will be slightly soft in center but will harden as they cool). Remove from baking sheet; cool on wire rack.