Preheat the oven to 400 degrees.
Butter a 14 x 18inch baking sheet with 1 tablespoon of the butter.
Cream the remaining butter with 1/2 cup of the sugar until light and fluffy. Beat in the egg yolk and vanilla. Mix in the sifted flour and cocoa.
Using your fingers, which have been run under cold water and dried, spread the batter over the baking sheet, completely covering it to the edges.
Beat the egg white until stiff and spread it over the batter. Combine the cinnamon with the remaining 1/4 cup sugar, and sprinkle it over the egg white.
Bake for about 10 minutes. Remove from the oven and immediately cut the pastry into about 24 diamond, square, or oblong shapes.
With a metal spatula, carefully remove the cookies from the sheet and cool.
c.1996, M.S. Milliken & S. Feniger, all rights reserved