Grease twelve to fourteen 2-1/2-inch muffin cups or line with paper bake cups; set aside. In a small mixing bowl stir together the 1/3 cup brown sugar and sour cream; stir in pecans. Set aside.
In a medium mixing bowl combine flour, baking powder, cinnamon, baking soda, salt, nutmeg, and cloves. Make well in center of dry mixture.
In another medium mixing bowl combine egg, buttermilk, pumpkin, the 2/3 cup brown sugar, and melted butter. Add pumpkin mixture all at once to the dry mixture. Stir just until moistened (batter should be lumpy).
Spoon batter into prepared muffin cups, filling each almost full. Spoon about 2 teaspoons of the pecan mixture on top of each muffin. Bake in a 375 degree F. oven for 20 to 25 minutes or until done. Cool in muffin cups on a wire rack for 5 minutes. Remove from muffin cups; serve warm. Makes 12 to 14 muffins.