Instructions:
Preheat Oven: Set the oven to 350°F (175°C) and grease a 9×13 inch baking pan.
Make the Cake Batter:
In a bowl, whisk together the flour, sugar, baking powder, and salt.
Add milk, eggs, vanilla, and melted butter. Mix until smooth. Pour into the prepared pan.
Prepare the Filling:
In a separate bowl, combine softened butter, brown sugar, cinnamon, and nuts (if using).
Add Filling to Cake:
Drop spoonfuls of the filling mixture evenly over the cake batter. Use a knife to swirl it through the batter to create a marbled effect.
Bake:
Bake for 25-30 minutes or until a toothpick comes out clean.
Make the Glaze:
While the cake is baking, whisk together powdered sugar, milk, and vanilla until smooth.
Glaze the Cake:
Once the cake is out of the oven, drizzle the glaze over it while it’s still warm.
Cool and Serve:
Let the cake cool slightly, then enjoy warm or at room temperature.