Preheat your oven to 350°F (175°C). Grease a 9×13 inch baking pan to prevent sticking.

In a large bowl, mix together melted butter, eggs, and sugar until well blended. Add flour, vanilla, baking powder, and salt to the bowl. Stir until just combined. Gradually add milk, mixing until the batter is smooth and free of lumps.

Pour the batter into the prepared baking pan. Spread it evenly across the pan.

In a small bowl, combine melted butter, brown sugar, flour, and cinnamon. Mix until smooth. Drop spoonfuls of the topping mixture evenly over the batter in the pan. Use a knife to swirl the topping into the batter, creating a marbled effect.

Place the pan in the preheated oven. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.

While the cake is baking, whisk together powdered sugar, milk, and vanilla in a small bowl until smooth. Aim for a glaze consistency similar to pancake syrup.

Once the cake is done, remove it from the oven and let it cool slightly. While the cake is still warm, drizzle the glaze over the top. Allow it to set as the cake cools.

Serve the cake warm for a comforting treat or at room temperature for convenience.