Position rack in center of oven; preheat to 375°F
Lightly grease or butter a heavy large baking sheet.
Mix flour, baking powder, ginger, cinnamon, salt and cardamom in medium bowl to blend . Add butter and rub in with fingertips until mixture resembles coarse meal.
Whisk pumpkin, 1/4 cup cream, brown sugar, 2 tablespoons honey and lemon peel in another medium bowl to blend.
Add pumpkin mixture and chopped nuts to dry ingredients and stir until incorporated (dough will be moist).
Turn dough out onto floured surface and knead gently until smooth, about 8 turns. Roll out dough to 3/4-inch thickness. Using floured 2-inch-diameter cookie cutter, cut out rounds. Reroll scraps to 3/4-inch thickness; cut out additional rounds.
Place biscuits on prepared baking sheet, spacing evenly.
Whisk 2 tablespoons cream and 2 tablespoons honey in small bowl. Brush on tops of biscuits biscuits. Garnish each with 1 walnut half.
Bake biscuits until light golden and tester inserted into center comes out clean, about 25 minutes. Transfer biscuits to rack and cool 15 minutes.
Serve warm or at room temperature, with butter.