Preheat oven to 400°F. Grease the bottoms of twelve 2-1/2-inch muffin cups; set aside.
In a medium bowl stir together flour, fresh or ground ginger, baking powder, allspice, baking soda, and salt. Using a pastry blender, cut in butter until mixture resembles coarse crumbs. Make a well in center of flour mixture.
In another medium bowl combine egg, sour cream, milk, brown sugar, and molasses. Add egg mixture all at once to flour mixture. Stir just until moistened (batter should be lumpy). Spoon batter into the prepared cups, filling each nearly full.
In a small bowl combine granulated sugar and crystallized ginger. Sprinkle over muffin batter.
Bake for 18 to 20 minutes or until golden brown and a toothpick inserted near the centers comes out clean. Cool in pan on a wire rack for 5 minutes. Remove from pan; serve warm.