Preheat the oven to 350°F (180°C) and grease a 9x13-inch baking pan.

In a large mixing bowl, use an electric mixer or stand-up mixer to combine the flour, sugar, salt, baking powder, milk, eggs, and vanilla extract until well mixed.

Slowly stir in the melted butter until fully incorporated into the batter.

Pour the batter into the greased baking pan.

In a separate large mixing bowl, use a spoon to mix together the softened butter, brown sugar, flour, cinnamon, and chopped nuts (if using) until well combined.

Drop spoonfuls of the cinnamon mixture evenly over the cake batter, then use a knife to marble/swirl through the cake.

Bake the cake for 25-30 minutes or until a toothpick inserted into the center comes out nearly clean.

While the cake is baking, make the glaze by whisking together the powdered sugar, milk, and vanilla extract in a large mixing bowl until smooth.

Once the cake is done, remove it from the oven and allow it to cool for a few minutes.

Drizzle the glaze over the warm cake.

Serve the cake warm or at room temperature.