Preheat oven to 350 degrees F. Spray a 9 x 13 inch glass baking pan with cooking spray or Baker's Joy. Set aside.
In an electric or stand mixer add the flour, salt, sugar, baking powder, milk, eggs, and vanilla. Once combined, slowly stir in the melted butter. Pour into the prepared 9x13 baking pan.
For topping, In a large bowl mix the 2 sticks of butter, brown sugar, flour and cinnamon together until well combined and creamy. Drop evenly over the batter by the tablespoonfuls and use a knife to marble/swirl through the cake.
Bake at 350 for 28-32 minutes or when a toothpick inserted near the center comes out nearly clean.
FOR GLAZE: In a medium bowl, mix the powdered sugar, milk and vanilla together with a whisk. Drizzle evenly over the warm cake. Serve warm or at room temperature.