Preheat the oven to 375 degrees. Oil the muffin tin or line it with paper cups.
Rinse and sort the cranberries. Coarsely chop the cranberries and walnuts by hand or in a food processor. Add the brown sugar, ginger, and cinnamon; mix well and set aside.
Whisk together the pumpkin, eggs, oil, buttermilk, molasses, grated ginger root, cinnamon, and brown sugar in a mixing bowl. Sift together the flour, baking powder, baking soda, and salt in a separate bowl. Combine the wet and dry mixtures, stirring until just blended; the batter will not be completely smooth.
Fill the prepared muffin cups about 3/4 full and top each muffin with about 1 tablespoon of the cranberrynut mixture. Bake for about 30 minutes, until a knife inserted in the center of a muffin comes out clean.