With an electric mixer combine flour, sugar, salt, baking powder, milk, eggs, and vanilla, until well mixed.
Slowly stir in 4 T melted butter.
Pour batter into a greased 9×13” pan.
In a large bowl, mix the 2 sticks butter, brown sugar, flour, cinnamon, and nuts until well combined.
Drop the mixture evenly over cake batter by the tablespoon and use a knife to marble into the cake batter.
Bake 25-30 minutes, at 350° or until a knife inserted into the center comes out clean.
Place powdered sugar, milk, and vanilla in a large bowl.
Whisk until smooth. Drizzle over warm cake. Serve warm or at room temperature.