Set your oven to 350°F and prepare a 9×13 inch baking dish by greasing it. In a large mixing bowl, combine the flour, granulated sugar, salt, baking powder, milk, eggs, and vanilla extract. Blend until well mixed, then slowly incorporate the melted butter into the batter. Pour the batter into your prepared pan.

In a separate bowl, mix the softened butter, brown sugar, cinnamon, and nuts (if using). Drop spoonfuls of this mixture over the cake batter, then use a knife to gently swirl it into the batter to create a marbled effect.

Place the pan in the oven and bake for 25-30 minutes, or until a toothpick inserted into the center comes out almost clean.

For the glaze, whisk together the powdered sugar, milk, and vanilla in a medium bowl until smooth. Once the cake is done baking, drizzle the glaze over the warm cake. Serve warm or at room temperature.