Preheat oven to 350 degrees. Spray 9 X 13 glass baking pan with cooking spray. Set aside.
Use mixer add flour, salt, sugar, baking powder, milk, eggs, and vanilla. Once combined well, slowly stir in the melted butter, pour into baking dish.
In large bowl, cream butter, brown sugar, flour, & cinnamon until combined & creamy. Drop evenly over batter by tablespoons & use knife to marble/swirl through cake. Bake @ 350 for 35-40 minutes.
In medium bowl mix powdered sugar, milk, & vanilla with a whisk. Drizzle evenly over warm cake. Serve at room temperature or warm.