Heat the oven to 400 degrees F. Prepare the batter: Lightly brush a 20-inch nonstick deep-dish pizza pan or cake pan with butter. Dust with flour, and shake to remove excess. Lightly brush the outside of a small ramekin with butter. Dust with flour, and shake to remove excess. Place prepared ramekin dish in the center of the prepared pizza pan.
In a large mixing bowl combine, flour, sugar and baking powder. Whisk to combine. In another mixing bowl, whisk together melted butter, milk, eggs, egg yolks, zest, and vanilla. Add butter mixture to dry ingredients. Whisk together until all of the flour is incorporated.
Spoon the batter around the prepared pan, working form the inside of the pan to the outside. You will not fill the pan completely. There will be a border from the edge of dough to pan.
Prepare topping: In a small bowl mix together egg white and sugar for topping. Sprinkle dough with crumbled topping. Bake until golden brown, about 20 to 25 minutes. Remove the cake from the oven. While the cake is still warm, using 2 forks gently lift the ramekin out of the center of the cake. Let cool before serving.
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