Ingredients for 4 - 6 servings:
1/2 stick butter
1/3 cup whipping cream
4 large eggs
1-1/4 cup sugar, divided
3/4 cup fresh lemon juice
grated zest of 2 lemons
1/2 cup egg whites at room temp.
1/2 lemon thinly sliced (optional)
Combine butter and cream in a quart saucepan, and heat until the butter melts. Whisk together eggs, 1 cup of sugar, lemon juice and grated zest in a mixing bowl. Pour the hot cream into the mixing bowl, whisking constantly. Return the combined liquid to low heat, and stir until it thickens noticeably and coats a metal spoon as well as the bottom and sides of the pan (180 degrees). Sieve the custard into a clean bowl. Wipe lightly with the open end of a stick of butter to coat the surface. Cover the bowl with plastic, and let it cool completely.
Beat the egg whites to soft peaks. Add the remaining 1/4 cup sugar, tablespoon at a time continuing to beat until the whites are stiff and meringue-like. Stir the stiffened whites into the cool lemon custard. Fold in the remaining 2/3's in two installments.
Chill thoroughly before serving on the same day, or freeze overnight and serve scoops of custard with a thin slice of lemon the next day.