Beat together the butter and sugar until light and fluffy, then mix in the eggs and pumpkin puree. Gradually stir in the vanilla, flour, baking powder, salt, and pumpkin pie spice. Fold in the toffee bits.

Shape the dough into a 10x4-inch rectangle, wrap it in plastic wrap, and refrigerate for 1 hour.

Slice the chilled dough into two loaves, place on a baking sheet, and bake at 350°F for about 28 minutes, until set and lightly golden.

Cool the loaves for 10 minutes, then slice into 12 pieces each and lay cut-side down on the baking sheet.

Return to the oven for another 10 minutes, or until lightly golden and firm.

Melt white chocolate, drizzle over cooled biscotti, and let set before serving.