1. In an electric or stand mixer mix the flour, salt, sugar, baking powder, milk, eggs and vanilla. Once combined well, slowly stir in melted butter. Pour batter into a greased 9 x 13 inch baking pan.
2. In a large bowl, mix the 2 sticks of softened butter, brown sugar, flour, cinnamon and nuts until well combined. Drop evenly over cake batter by the tablespoonfuls and use a knife to marble/swirl through the cake.
3. Bake for 25-30 minutes or until toothpick comes out nearly clean from center.
4. Place powdered sugar, milk and vanilla in a large bowl. Whisk until smooth. Drizzle over warm cake. Serve warm or at room temperature. Enjoy!