Combine all streusel ingredients in a small bowl. Stir together until crumbly and set aside.
Preheat oven to 350 degrees and line 2 muffin tins with 24 paper liners.
Sift together flour, baking powder, baking soda, cinnamon, nutmeg and salt in a large mixing bowl. Whisk together for 30 seconds to fully combine then set aside.
In a separate mixing bowl, blend sugar and butter together until combined. Add eggs and blend with the butter and sugar. Add milk, vanilla and pumpkin puree. Mix only until combined.
Combine wet and dry ingredients and fold until the flour is completely combined, but don’t overwork the batter! Fold in nuts.
Scoop batter into muffin liners, filling each one about ¾ full. Sprinkle streusel topping over each muffin. Bake 18–20 minutes or until a toothpick in the center comes out with a few moist crumbs attached. Remove the muffins from the oven and cool 5 minutes before removing them from the pan and transferring to a wire rack to cool completely before adding the glaze.
While the muffins are cooling, prepare the glaze by melting butter in a medium microwave-safe bowl for approximately 30 seconds. Add in the powdered sugar, vanilla and maple syrup and whisk together to form a glaze. If it is too thick, stir in a few drops of milk until you reach the desired consistency.
Spoon glaze over each cooled muffin—one at a time—and allow the excess to drip off. Immediately top with a sprinkling of crushed nuts. Allow the glaze to set approximately 2 minutes then have at it!
One Last Thing
Make the streusel before you start making the muffins because if you let the baking soda in the muffins sit too long the bubbles will dissipate, causing flat muffins!