Step 1

Preheat oven to 325 degrees F. Coat an 8-inch square baking dish with cooking spray.

Step 2

In a medium bowl, beat egg whites until stiff peaks form; set aside.

Step 3

In a large bowl, combine egg yolks and sugar and beat until smooth. Add butter and vanilla; mix well. Beat in flour, then slowly add milk until well combined. Slowly fold in egg whites; do not over mix. Pour into baking dish.

Step 4

Bake 45 to 50 minutes, or until set in center and golden brown on top. Let cool.