Beat until white
Butter a copper baking sheet or a shallow paper casing made from a half sheet of paper. Pour in the mixture, smooth it out, and bake. When the batter is half cooked, remove from the oven, mark out rectangles, and return to the oven to finish baking. Take out of the oven, cut into pieces with a thin knife, and remove from the baking sheet. Hollow out the bottoms slightly, leaving the edges intact, and fill with wine custard. Level off and stick together so that the custard is not visible. Set in a warm oven; then arrange on a napkin on a platter.