1: Preheat the oven to 350 degrees F.
2: In a mixer, cream the butter for 2 minutes till light and smooth.
3: Add pumpkin puree, continuing to mix. Add eggs one at a time and then the yolk, beating after each addition.
4: Add sugar, vanilla and rum (if using).
5: In a separate bowl, combine the dry ingredients.
6: With the mixer on low, alternate dry ingredients and sour cream: adding ⅓ cup at a time of the dry mixture and 2 tablespoons of the sour cream to the pumpkin base.
7: Pour into a well greased loaf pan.
8: Prepare the topping by combining the flour, nuts, brown sugar, salt, cinnamon and clove. Pulse several times while adding butter until no dry spots remain.
9: Use a knife to push the topping ingredients into the bread to create a marbled effect.
10: Cook for 50 minutes or until a cake tester or toothpick comes out clean.
11: Remove from the oven and cool for 10 minutes in the pan before removing to a cooling rack to finish cooling.
