Cream the softened butter and add the sugar in a stream. Continue beating until mixture whitens. Beat in the lemon zest and rum, then egg whites, one at a time, beating smooth between each addition. Mix the almonds and flour together and stir them into the batter by hand.
2
Pipe the batter on paper-lined pans in 1-inch mounds using a 1/2-inch plain tube. Bake the cookies at 350 degrees about 12 to 15 minutes. Cool the cookies on the paper.
