Try this with white peaches, if available, for a subtle variation on the original. PREHEAT THE OVEN TO 180ºC and set a rack in the middle level. Rinse, halve and pit the peaches. Puree 2 of the peach halves in a food processor. Place the puree in a bowl and add the sugar, crushed macaroons and the egg yolk. Cover each peach half with this filling and place the peach halves in a buttered baking dish. Sprinkle the remaining butter over the peaches and bake for about 30 minutes, until the peaches are baked through and the filling is a deep golden color. Serve hot or at room temperature.