1. For the streusel topping: Combine the pecans, brown sugar, flour, pepitas, butter and salt. Squeeze into small clumps on a baking sheet and refrigerate until the streusel is chilled and firm, about 30 minutes.
2. For the muffins: Preheat the oven to 350 degrees F. Lightly grease the top of the muffin tray to keep the muffins from sticking. Line a 12-cup muffin tin with your favorite liners.
3. Combine the all-purpose flour, brown sugar, whole wheat flour, baking powder, ginger, salt, allspice, baking soda and clove in a large bowl.
4. Whisk together the pumpkin puree, buttermilk, eggs and butter in a separate small bowl.
5. Fold the wet ingredients into the dry until just combined (don't fret if the batter has lumps this means your batter isn't over-mixed).
6. Fill each muffin liner 3/4 of the way full. Evenly divide the streusel among the muffins, mounding in the center.
7. Bake until the topping is golden and crunchy and a toothpick inserted in the muffins comes out clean, rotating the trays about halfway through, 25 to 28 minutes. Let rest in the hot muffin pan 3 minutes then transfer to a cooling rack.
Use your leftover pumpkin puree to make Pumpkin Frosting for another type of muffin or quick bread: Beat together 1 cup pumpkin puree, 8 ounces soft cream cheese, 3/4 cup confectioners' sugar, 1 teaspoon orange zest, 1/2 teaspoon ground cinnamon and a pinch each allspice and salt until smooth. This will be enough to frost about 12 cupcakes or muffins.