Preheat oven to 325° F. Grease the bottom of a 9-inch x 5.25-inch bread pan. Have three medium/large bowls ready: one to mix the dry ingredients and the others to divide the batter. You will also need a stand mixer or a hand mixer and bowl.
Whisk together the flour, sugar, baking soda, baking powder, cinnamon and salt in one of the bowls.
Beat together the eggs, pumpkin puree, oil, sour cream and vanilla in a stand mixer or using a hand mixer.
Add the dry ingredients to the wet mixture in two or three additions, and mix together only until just combined. (Do not over-mix.)
Divide the batter and add the flavors:
Divide the batter between evenly between two bowls.
Add the white chocolate chips and nutmeg to one of the bowls. Stir together by hand.
Add the cocoa and coffee to the second bowl. Stir together by hand.
Layer the batters in the pan:
Begin with the chocolate batter. Add ⅔ of a cup to the prepared pan and use a rubber spatula to gently spread the batter over the bottom. Sprinkle some of the semisweet chocolate chips over the batter.
Next, add ⅔ of a cup of the white chocolate chip batter, and use a rubber spatula to gently and evenly spread it over the first layer to the edges.
Repeat these layers: chocolate batter, a few semisweet chocolate chips and then white chip batter, until all of both batters are used.
Place the pan in the oven and bake it for a total of 1 hour 45 minutes. Halfway through baking tent the top of the pan very loosely with foil to prevent the loaf from over-browning.
Remove the foil from the bread for the last 5 minutes of baking. A tester inserted into the loaf should come out clean.
Allow the bread to cool completely in the pan.
Run a knife along the edges to loosen them and then turn the cooled loaf out of the pan. Slice and serve.
Store the bread tightly wrapped at room temperature for up to 4 days.