Chocolate Wafers: Set 2 racks in the middle and upper third of the oven and preheat to 375 degrees F. In a food processor or the bowl of an electric mixer, thoroughly mix together the flour, cocoa, baking soda, baking powder, salt, and sugar. While pulsing on low speed, add the butter, then the egg. Process or beat until the dough is thoroughly blended and massed together. Drop rounded teaspoons of batter onto nonstick or parchment-lined cookie sheets at 2-inch intervals. With moistened fingers, round out the cookies and flatten them a little. Bake for 9 minutes, turning the pans once for even baking, until the cookies are set. Set the cookie sheets on a rack to cool.
In a mixing bowl, whip the cream to soft peaks, about 1 1/2 minutes. Add the confectioners' sugar and vanilla, and continue whipping until stiff but smooth, about 1 minute. Spread the wafers evenly with the whipped cream, about a 1/4 inch thick, and set in stacks of 8. Turn the stacks on their sides and line them up, one after the other, like the wheels on an eighteen-wheeler, 4 rows deep. Frost the top and sides with the remaining whipped cream to form a loaf. Refrigerate for at least 3 hours, until firm. To serve, dust lightly with cocoa or cookie crumbs. Slice with a serrated knife dipped in hot water.