01 - Preheat your oven to 350°F (175°C). Generously grease a 9x13-inch baking pan.
02 - In a large mixing bowl, cream together the softened unsalted butter and granulated sugar until the mixture achieves a light and fluffy consistency.
03 - Add the large eggs one at a time, ensuring each is fully incorporated before adding the next. Mix in the vanilla extract.
04 - In a separate bowl, whisk together the all-purpose flour, baking powder, and fine salt.
05 - Gradually add the dry ingredients to the wet mixture, alternating with the whole milk. Begin and conclude with the dry ingredients. Mix until just combined, taking care not to overmix.
06 - Transfer the cake batter into the prepared 9x13-inch baking pan and spread evenly to create a smooth surface.
07 - In a small bowl, combine the packed brown sugar and ground cinnamon. Stir in the melted unsalted butter until a well-blended mixture forms.
08 - Dollop spoonfuls of the cinnamon mixture evenly over the cake batter. Using a knife, gently swirl the cinnamon mixture into the batter to create distinct ribbons.
09 - Bake for 32 to 36 minutes, or until a wooden toothpick inserted into the center of the cake emerges clean.
10 - Allow the cake to cool in the pan for at least 15 minutes before proceeding.
11 - For the glaze, whisk together the powdered sugar, milk, and vanilla extract in a bowl until a smooth, pourable consistency is achieved. Drizzle the glaze over the still-warm cake before serving.