Preheat oven to 325. In large mixing bowl mix butter and sugar until creamy. Mix in pumpkin, sour cream, eggs, and vanilla. Set aside.
Place dry ingredients in a mixing bowl and stir to combine. Add flour mixture to wet mixture gradually and mix on medium speed until thoroughly combined.
Divide batter between 2-9" round baking pans that have been coated with cooking spray. Sprinkle each cake with 1/4 cup of candied walnuts. Bake for 25-30 minutes or until cake is set and a toothpick comes out dry when inserted in the center of the cake.
When the cake is done, make the frosting. Place combined sugar and butter in a heavy saucepan.
Cook until sugar and butter is melted, stirring only occasionally until mixture comes to a boil. Boil 2-3 minutes then add milk, vanilla, salt, and Karo syrup and boil another 1-2 minutes.
The mixture will begin to thicken. Remove from heat and stir until no longer bubbly, the frosting will be shiny and easy to pour.
Drizzle evenly over both coffeecakes. Cool, cut, and enjoy!