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.
Cook's Notes: To save some time, toast your pecans and pepitas together on the same baking sheet. The streusel top is crunchy and delicious but be sure not to snub the stump!
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.