Grease a 9- by 13-inch pan and set aside. For the topping, mix together melted butter, brown sugar, flour, cinnamon, and nuts. Set aside.
For the cake, in a large bowl, cream together butter, granulated sugar, and brown sugar. Add eggs one at a time, blending well after each. In a separate bowl, mix together flour, baking powder, baking soda, cinnamon, and salt. Add alternately with buttermilk to creamed mixture. Pour batter into prepared pan. Sprinkle batter with topping mixture. Cover and refrigerate overnight. In the morning, bake in a preheated 350-degree oven for 30 to 35 minutes.
To make the glaze:
In a small bowl combine glaze ingredients and stir until smooth. Drizzle glaze over entire cake.