Modified from https://celebratingsweets.com/pumpkin-crumb-muffins-with-cinnamon-icing/
In a medium bowl, combine sugars, cinnamon, salt, and melted butter. Whisk until combined. Add flour, and stir until the flour is combined. Set aside.
Preheat oven to 350°F. Grease a 12 cup muffin tin, or line with paper liners. In a medium bowl, combine flour, cinnamon/spice, baking soda, baking powder, and salt. In a large bowl, whisk eggs, brown sugar, oil, pumpkin puree and vanilla, until combined. Add flour mixture, and stir until combined (I use a rubber spatula), being careful not to over-mix. Divide the batter between 12 muffin cups. Pinch off small pieces of the crumb topping and scatter them over the tops of each muffin. Bake for approximately 20 minutes, until a toothpick inserted into the center of the muffins comes out clean. Place the pan on a wire rack to cool for 10 minutes, then remove the muffins from the pan and place on the rack to cool completely.
Whisk all ingredients until smooth. Adjust the consistency by adding more powdered sugar (to thicken) or more milk (to thin). Use a small spoon to drizzle icing over the tops of the cooled muffins.
Feel free to swap up to half of the all purpose flour for white whole wheat flour.