Allow butter and eggs to stand at room temperature for 30 minutes.
Meanwhile, grease and flour two 8 cake pans.
In a bowl, stir together flour, baking powder, cinnamon, baking soda, ginger, salt, nutmeg and cloves until mixed. Set aside.
In a large mixing bowl with an electric mixer beat softened butter and shortening on high speed for 30 seconds. Add sugar and vanilla and continue mixing. Add eggs, one at a time, beating well after each addition.
In a small bowl, stir together buttermilk and pumpkin. Alternately add flour mixture and pumpkin mixture to butter and sugar mixture, ending with flour mixture. Beat on low speed just until combined. Pour into prepared pans. Batter will be thick. Use a spatula to spread evenly in pans or cakes will be lumpy.
Bake in a preheated 350°F oven for 30 to 35 minutes or until cake tests done. Cool in pans for 10 minutes then turn out onto wire rack to cool completely.
Melt butter in a small saucepan over medium heat. Reduce heat to medium low and continue cooking at a simmer until butter turns the color of light brown sugar. This will take a few minutes. Remove from heat and let stand at room temperature for 15 minutes.
Meanwhile, in a large mixing bowl combine powdered sugar with milk and vanilla. Add browned butter and beat with an electric mixer on low speed until combined. Beat on high speed, adding more milk as needed to get a spreading consistency.
Frost cake. If using, press toasted pecans around side of cake. Can take a sieve or sifter and dust the top with pumpkin pie spice if you wish.