Step 1

Heat the oven to 350 degrees F, with a rack in the middle of the oven. Line the bottom of loaf pan (8 1/2 by 4/12 inches) with a piece of parchment, and grease the bottom and sides with butter.

Step 2

Place the brown sugar, white sugar, egg, egg yolk and canola oil in a medium bowl and whisk it together. Add the pumpkin purée, sour cream and vanilla, and whisk it well to combine. Set aside.

Step 3

Sift together into a separate medium bowl the whole wheat flour, all-purpose flour, baking soda, salt, cardamom, nutmeg, cinnamon, cloves and white pepper. Give it a whisk to make sure they’re mixed well, then use a rubber spatula to fold the dry mixture into the wet ingredients. Give it a quick gentle whisk to just combine.

Step 4

Pour the batter into the prepared loaf pan, and sprinkle the top with the turbinado or demerara sugar.

Step 5

Bake 25 minutes, then rotate the pan. Continue baking for about another 30 minutes, until the bread is well browned, cracking on top and firm to the touch. Transfer the pan to a wire rack to cool for 5 minutes, then run a thin knife around the edge and carefully turn the loaf onto the rack to continue cooling. Serve warm or at room temperature. It keeps beautifully in an airtight container or zipper bag for at least 3 days.