Instructions

• Preheat oven to 350F degrees. Spray 9x13-inch baking dish with nonstick cooking spray (I like the kind that has flour in it.) In a large bowl (or the bowl of your stand mixer), combine 3 cups all-purpose flour, 1 cup white granulated sugar, 4 teaspoons baking powder, 2 large eggs, 2 teaspoons vanilla extract and 1 1/2 cups milk.
• While your mixer is running, slowly add 1/2 cup (1 stick) salted butter, melted. Mix just until combined (overmixing flour in baked goods can make it tough and rubbery.)
• Spread this batter evenly into your prepared baking dish.
• In a small bowl, combine 3/4 cup salted butter, softened to room temperature, 1 cup packed light brown sugar, 2 Tablespoons all-purpose flour and 1 Tablespoon ground cinnamon. Stir until combined well.
• Drop the cinnamon filling by spoonfuls onto the cake batter.
• Take a butter knife and make swirly, marble-effect patterns all around the cake. Drag the knife through both the cinnamon and cake batter.
• Bake the cake for about 35-40 minutes (it took about 40 minutes in my oven), until a knife inserted into the center comes out clean.
• Whisk together 2 cups powdered sugar, 5 Tablespoons milk and 1 teaspoon vanilla extract in a bowl. If you want it thicker, add more powdered sugar and if you want it thinner, add more milk.
• Pour the glaze over the warm cake. This cake can be served warm or at room temperature but I think it's easier to slice if you allow it to cool first.