Preheat oven to 190° C / 375° F.

Line two half sheet rimmed baking trays with parchment or silicone baking mats. Set aside.

In a large mixing bowl or the bowl of a stand mixer, mix pumpkin purée, sugars, butter, and egg on medium-high speed until well-combined.

In a separate bowl, stir together flour, baking powder, salt, and spices. Add to wet ingredients in 3 additions, mixing well after each addition. Dough will be sticky.

With floured hands, transfer dough to lightly floured countertop.

Divide the dough into two equal portions and shape into 10-inch x 2-inch logs.

Place logs on one of the prepared trays, allowing 3-4 inches of space in between.

Bake logs for 25 minutes. Remove from oven and reduce oven temperature to 325° F / 162° C.

Cool on trays for15 minutes.

Transfer logs to a chopping board. Use a serrated knife to slice diagonally into 1/2-inch slices.

Arrange biscotti slices on both prepared trays, places the slices upright and dividing them equally between the two trays. Bake for another 20-25 minutes, or until dry.

Cool completely on trays.

Melt chocolate over a bain marie or double boiler, or in a microwave-safe bowl at medium temperature, stirring frequently.

Dunk biscotti in melted chocolate, drizzle with a spoon, or pipe in zigzags over biscotti cookies. Finish with a sprinkling of Demerara sugar.

Set aside and allow chocolate to set at room temperature.

Layer biscotti in an airtight container between sheets of parchment or wax paper. Store at room temperature for up to 5 days, or freeze for up to 3 months.