Preheat the oven to 350°F. Lightly grease baking sheet, and set aside.
With an electric mixer on medium speed, beat the softened butter, sugar, spices, baking powder, and salt. Add in the egg and pumpkin purée, and beat until well blended.
With your mixer on a low speed, slowly add the flour. Mix until just combined.
Divide the dough in half. Place one half onto the greased baking sheet and shape it into a 10″ x 2 1/2″ log. Repeat with second half of the dough. Make sure to pat them into long rectangles. Smooth out the top and sides with yours hands. If the dough is a little too sticky, add some flour to your hands.
Sprinkle the coarse white sparkling sugar on top of both logs. Bake the dough for 25 minutes. Remove it from the oven and let sit 10 mins.
Starting at one end of each log, cut into 1-inch biscotti pieces working your way down. Repeat with second log. Arrange all biscotti pieces on their sides.
Bake another 20-25 minutes. Remove from oven, and place on a wire rack. Let cool completely before applying chocolate.
In a wide, shallow bowl, add dark chocolate and 1 tablespoon heavy whipping cream. Microwave for 30 seconds, stir with a rubber spatula. Microwave an additional 30 seconds, and stir until melted through.
Lightly dip the bottom sides of biscotti in the chocolate. Place upside down on a wire rack until hardened and set.
If your chocolate does not harden completely, place biscotti in the refrigerator for roughly 30 minutes.
Biscotti will keep for 5-7 days in the refrigerator or an air tight container.