Instructions

• Preheat the oven to 350°F (175°C). Grease a 9"x13" cake pan (or line it with parchment and grease the sides and bottom). Set the pan aside.
• In a large bowl, sift together 3 cups all-purpose flour, 1/4 teaspoon salt, and 4 teaspoons baking powder. Add 1 cup granulated sugar and whisk to combine.
• In a separate bowl, whisk together 1 1/2 cups milk, 2 large eggs, and 2 teaspoons vanilla extract until blended.
• Slowly pour the wet mixture into the dry ingredients and whisk until mostly smooth.
• Gradually whisk in 1/2 cup melted unsalted butter until the batter is smooth and uniform.
• Spread the batter evenly in the prepared 9"x13" pan. Set the pan aside.
• In a medium mixing bowl, beat 1 cup unsalted butter (softened to room temperature) with an electric mixer until creamy.
• Add 1 cup packed light brown sugar, 2 tablespoons all-purpose flour, and 1 tablespoon ground cinnamon to the butter. Beat until the mixture is fluffy and comes together, about 2 minutes (it may look crumbly at first).
• Drop or spread the cinnamon filling over the cake batter, leaving about a 1-inch border around the edges. Use an offset spatula or rubber spatula to gently swirl the filling into the batter to create ribbons—do not fully mix it in.
• Bake the cake for 28 to 32 minutes, or until a toothpick inserted into the cake portion (avoiding the filling ribbons) comes out clean or with a few moist crumbs.
• Remove the cake from the oven and cool in the pan on a wire rack for 15 minutes.
• While the cake cools, sift 2 cups powdered sugar into a medium bowl. Add 1 teaspoon vanilla extract and 5 tablespoons milk, then whisk until the glaze is smooth and has a drizzling consistency.
• Pour the glaze over the still-warm cake and spread evenly.
• Allow the glaze to set, then cover and store the cake at room temperature for up to 3 days.