A thin cake instead of cookies (a trick from a Martha Stewart magazine) seems to be easier and less messy when making ice cream sandwiches. Cookies are often too thick making them hard to handle and hard to eat when frozen.
1. In a medium bowl, whisk butter with sugar until light. Whisk in egg. Combine flour with sifted cocoa. Whisk into egg mixture. Spread batter on a 9"x13" baking pan that has been buttered and lined with parchment paper. (Donâ€™t worry that batter barely covers the pan.) Bake in a preheated 325F oven 12 to 15 minutes until the surface of the cake does not stick to your fingers when gently pressed. Cool on rack. Run a knife around the edge and turn cake onto another piece of parchment paper.
2. To assemble, cut cake in have crosswise. Spread ice cream over cake (bottom side up). Invert second piece on top. Wrap well and freeze.
3. When ready to serve, unwrap and cut into 8 pieces.