In an electric or stand mixer mix the flour, salt, sugar, baking powder, milk, eggs and vanilla. Once combined well, slowly stir in the 1/2 cup melted butter. Pour batter into a greased 9 x 13 inch baking pan.
In a large bowl, mix the 1 cup of softened butter, brown sugar, flour, cinnamon and pecans until well combined. Drop evenly over cake batter by the tablespoonfuls and use a knife to marble/swirl well through the cake.
Bake at 350 degrees for 25-30 minutes or until toothpick comes out nearly clean from center. You want to make sure it's done. I like most things underdone but cake is not one of them.
In a large bowl, beat the butter, cream cheese, powdered sugar, milk and vanilla until smooth. Add more milk as needed to get to your desired consistency. Spoon over cake or fill a ziplock bag with the frosting and snip the corner to drizzle on. Serve warm or at room temperature.