2lemonszested and juiced (1/4-1/3 cup juice, 2 tablespoons zest)
Preheat oven to 350°F/175°C
Cream the butter and sugar well. Add the egg yolks one at a time, mixing after each addition. Then add the flour, then lemon zest, and juice. Whisk in the milk and mix well.
In a separate bowl, beat the egg whites until stiff. Fold gently into the lemon mixture until incorporated. Pour into an 8- or 9-inch pie plate or cake pan, or evenly among four 1-cup ramekins.
Bake for about 40 minutes, until very lightly browned around the edge and mostly set. You can use a toothpick to see if top cake layer is done, but remember that the bottom should be like custard. Sprinkle with powdered sugar and serve warm with sweetened whipped cream.
For thicker layers, double the recipe and use a 9-inch pan or springform.