Have all ingredients at room temperature. Preheat the oven to 375 F with the rack in the middle position. Butter a 12-cup muffin tin.
To make the streusel: Stir together the flour, brown sugar, ginger and salt in a small mixing bowl. Using a pastry blender or 2 forks, cut in the butter until it creates pea-sized crumbs. Fold in the chopped pecans and set aside.
To make the muffins: Sift together the flour, ginger, baking powder, salt and baking soda in a medium mixing bowl. Add the pecans to the dry ingredients and set aside.
In a large mixing bowl, whisk together the buttermilk, melted butter, sugar, eggs, fresh ginger and vanilla. Add the dry ingredients to the buttermilk mixture, and, using a rubber spatula, fold together until no streaks of flour remain. Do not over mix. Gently fold in the drained cranberries, just until incorporated.
Spoon the batter into the muffin tins. Sprinkle the streusel over the tops of the batter. Bake until the muffins are golden brown and a toothpick inserted into the center of a muffins comes out clean, 20 to 25 minutes. Transfer to a wire rack to cool for 10 minutes. Release the muffins from the pan and serve.
Makes 1 dozen muffins.