Stir together the flour, brown sugar, and cinnamon. Pour in the melted butter and stir until coarse crumbs form. Fold in the pecans if using, then chill while you make the batter.

Preheat the oven to 425F. Line a 12-cup muffin tin with paper liners.

In a large bowl, whisk together the pumpkin puree, granulated sugar, brown sugar, oil, eggs, milk, and vanilla until smooth.

Add the flour, baking soda, baking powder, pumpkin pie spice, and salt. Stir until just combined. Do not overmix.

Divide the batter among the muffin cups, filling each nearly to the top. Spoon the chilled streusel over each muffin and press gently so it sticks.

Bake at 425F for 5 minutes. Without opening the oven, reduce to 350F and bake another 15 to 18 minutes, until a toothpick comes out with a few moist crumbs. Cool in the pan 5 minutes, then transfer to a wire rack.

Whisk the powdered sugar, maple syrup, and enough milk for a thin drizzle. Drizzle over the cooled muffins.