To make the crumb topping: combine sugars, cinnamon and salt in a medium bowl. Whisk in melted butter and add flour. Stir using a rubber spatula just until moist. The mixture will not look very crumbly yet. Spread out mixture on parchment paper to dry until crumbly ready to use.
To make the muffins: Preheat oven to 375° F. Place paper liners in a regular sized muffin pan and set aside. In a large bowl, beat the eggs, brown sugar, granulated sugar, pumpkin and oil until smooth. In a medium bowl, combine the flour, baking soda, baking powder, pumpkin pie spice and salt until combined. Add the flour mixture slowly to pumpkin mixture and mix well. Fill paper-lined muffin cups three-fourths of the way full. Top the muffin batter with the crumble topping until they're overflowing. Push it down slightly to keep it in place.
Bake the muffins for 10 minutes at 375 degrees then reduce the heat to 350 and bake for another 10-12 minutes, until muffins are set. Do not overbake. Cool in pan for 10 minutes before removing to a wire rack.
While muffins are cooling, make the brown butter maple drizzle. In a medium saucepan over medium-high heat, melt the butter. Allow to cook until brown specs begin to form at the bottom of the pan, about 3 minutes. Once formed, stir immediately and remove from heat. Add the powdered sugar, vanilla, maple syrup and water and stir vigorously until smooth. Add more water a tablespoon at a time until you get the desired consistency to drizzle over muffins. Using a spoon, drizzle over baked muffins and serve immediately or store in a air tight container for up to one week. Or freeze for one month.