Beat butter until softened. Add sugar, cocoa powder, and baking powder; beat until combined. Beat in eggs and as much of the flour as possible. Stir in remaining flour by hand along with the sliced almonds.
Divide dough into thirds. Shape each into a long log on a slightly greased cookie sheet. Flatten logs until 2 inches wide (about 1/4 to 1/2 inch high).
Bake at 375°F for 20-25 minutes. Logs will be fairly hard, but not completely. Cool for 45 minutes to an hour, then cut diagonally into 1/2 inch wide slices.
Place back on the cookie sheet with cut side down and cook in 325°F for 6 to 8 minutes on each side. Slices should be hard and brittle.Servings: 22, 44 slices