To make the streusel topping, combine sugars, cinnamon, and salt in a medium bowl. Whisk in melted butter and stir in the flour with a rubber spatula just until moist.
1/3 cup brown sugar, 1/3 cup granulated sugar, 1 teaspoon cinnamon, ¼ teaspoon salt, ½ cup unsalted butter, 1½ cups all purpose flour
Preheat oven to 375° F. Place paper liners in a regular sized muffin pan.
In a large bowl, whisk together the eggs, brown sugar, granulated sugar, pumpkin and oil until smooth.
2 eggs, 1 cup sugar, 1/2 cup brown sugar, 1/2 (15 oz) can pumpkin puree, 3/4 cup vegetable oil
Add the flour, baking soda, baking powder, pumpkin pie spice and salt and mix until just combined.
1 1/2 cups all purpose flour, 1 teaspoon baking soda, 1/2 teaspoon baking powder, 1/2 Tablespoon pumpkin pie spice, 1/2 teaspoon salt
Fill the paper-lined muffins just over three-fourths of the way full. Top the batter with the crumb topping until they're overflowing. Push it down slightly to keep it in place.
Bake for 7 minutes at 425 degrees then reduce the heat to 350 and continue to bake for another 10-12 minutes, until a toothpick inserted in the center comes out with a few moist crumbs.
Cool in the muffin pan for 15 minutes then transfer them to a wire rack. While they're cooling, whisk together the powdered sugar and milk. Place a piece of parchment paper under the cooling rack and drizzle the pumpkin muffins with icing.
Store pumpkin streusel muffins in an airtight container at room temperature for up 4 days or in the fridge for up to 1 week. Wrap with plastic wrap and freeze in a freezer bag for up to 3 months. Thaw overnight in the fridge and reheat.