Preheat the oven to 350°F. Line baking sheets with parchment paper or silpat baking mat.
In a large bowl, combine the butter, sugar, cocoa, eggs, flour, vanilla, and baking powder. Stir until well blended.
Drop rounded tablespoonfuls of the batter onto the prepared sheets, leaving at least 2 inches between them. You should have 16 cookies.
Bake for 8 to 10 minutes, or until set. Remove to racks to cool.
Remove the ice cream from the freezer to soften slightly at room temperature.
Place one cookie, flat side up, on a small sheet of plastic wrap. Place a scoop of ice cream on the cookie. Place a second cookie, flat side down, on top of the ice cream. Press the cookies together until the ice cream flattens and spreads to the edges of the cookies. Wrap the sandwich tightly in plastic wrap and place immediately in the freezer. Continue assembling the sandwiches and placing them in the freezer. When all the sandwiches are have been assembled and wrapped, place them all in the freezer bag and store in the freezer.
Nutritional values are approximate and based on 8 ice cream sandwiches using 1/2 quart of ice cream. Freeze leftovers promptly.