Place the eggs, milk, flour, sugar, salt, cinnamon, and vanilla into a blender. Cover, and blend for 15 seconds until fully mixed. Pour the blender contents into the prepared casserole dish, over the melted butter.
6 large eggs, 1 cup milk, 1 cup all purpose flour, 1 tablespoon sugar, ¼ teaspoon salt, 1 teaspoon cinnamon, 1 teaspoon vanilla extract