Preheat oven to 400 °F (200 °C). Cut the rolls into cubes and soak in the milk. Cream the butter with confectioner’s sugar until white. Add the egg yolk and lemon zest. Squeeze out some of the excess milk from the rolls and mix into the butter. Beat the egg whites to stiff peaks with granulated sugar and fold into the batter. Butter individual servings sized molds and sprinkle with granulated sugar. Fill and bake in a water bath for 30 minutes. Remove from molds and dust with confectioner’s sugar.
