Preheat oven to 350 degrees.
In a large bowl, mix the 2 sticks of softened butter, brown sugar, flour, cinnamon and pecans until well combined. Set aside.
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.
Drop topping evenly over cake batter by the tablespoonsful and use a knife to marble/swirl through the cake.
Bake at 350 degrees for 25-30 minutes or until toothpick comes out nearly clean from center
Place powdered sugar, milk and vanilla in a large bowl. Whisk until smooth. Drizzle over warm cake. Allow to cool before cutting.
Cut into 15 serving pieces. Serve warm or at room temperature.