Step 1

Preheat oven to 350 degrees F. Coat a 9- x 13-inch baking dish with cooking spray.

Step 2

In a medium bowl, cream butter and sugar. Add egg yolks one at a time. Add flour; mix well. Add lemon zest and juice, followed by milk; mix well.

Step 3

In another medium bowl, beat egg whites until stiff.  Gently fold egg whites into lemon mixture until completely incorporated. Pour into baking dish.

Step 4

Bake 40 to 45 minutes, or until very lightly browned and set. Let cool slightly, sprinkle with confectioners’ sugar, and serve warm.