Preheat the oven to 350ºF and line muffin cups with paper liners.
In a large bowl, mix all dry ingredients together: flour, granulated sugar, baking soda, baking powder, salt, cinnamon, nutmeg, pecans and brown sugar.
In another bowl, prepare liquid mixture by whisking eggs together until the yolks and whites are blended. Then add vanilla, oil and pumpkin puree.
Add the liquid mixture from step 3 to the dry ingredients mixture in step 2. Mix well with a wooden spoon.
Use a large spoon or an ice cream scoop to fill each muffin cup completely full.
Prepare the topping for the muffins by mixing pecans, brown sugar, cinnamon, flour together. Then add softened butter by cutting it into the dry ingredients with the fork until you have a good crumble topping. Sprinkle this mixture over muffins.
Using a spoon, spread the topping evenly over each muffin.
Bake until the muffins are springy to the touch and toothpick comes out clean, for 25 to 35 minutes. Start checking with the toothpick at 25 minutes.
Allow them to cool for 10 minutes, then turn out onto rack to cool completely. Please keep in mind that the larger the muffin cups, the longer it will take to bake them.
Sprinkle with confectionary sugar (optional).
This recipe makes 12 large muffins. For smaller muffins, divide the batter into 18 muffin cups and bake for 30 minutes.