Preheat the oven to 425 degrees F. Cut the butter into pats and put them in an ungreased 9x13 pan. Place the pan in the oven while it is preheating. Remove when the butter is melted.
Place the eggs, milk, all purpose flour, sugar, salt, cinnamon, and vanilla in a blender for 15 seconds until fully mixed. Pour into the prepared baking dish over the melted butter.
Bake for 20-25 minutes until the edges are golden brown and puffy. Slice into squares and serve immediately.