Preheat the oven to 350F with the top rack in the middle position. Line a 12-muffin pan with liners. You can also grease it.
Make the streusel crumble topping in a bowl by combining the flour, brown and white sugars, and melted butter. Mix it well; use your hands to combine it until it resembles coarse sand. Then, pinch some between your fingers to create larger clumps.
Make the muffin batter:
In a large bowl, combine the flour, sugar, baking powder, baking soda, cinnamon, pumpkin spice, and salt. Mix well with a whisk to distribute the ingredients.
In a medium bowl, whisk the eggs. Then, add the pumpkin pureé, milk, and melted (and cooled) butter (or a neutral oil). Pour the liquid mixture into the dry ingredients bowl and gently mix until combined. The batter is thick.
Scoop the batter into the muffin cups, filling each nearly to the top. Distribute the crumble topping generously over each muffin, then make a second pass to distribute the remaining topping, gently pressing it down so the crumbs stay on the muffins as they rise during baking.
Bake:
Bake the muffins for 20 to 22 minutes, until the tops are golden and a toothpick inserted in the middle comes out clean. Remove the muffin pan from the oven and let the muffins cool for 10 minutes before taking them out of the pan and placing them on a cooling rack to cool completely.
Store:
Muffins can be stored in an airtight container at room temperature (on the counter) for 1 day, in the refrigerator for up to 5 days, or in the freezer for up to 3 months.