Preheat the oven to 400°F (204°C) and position an oven rack in the center of the oven. Smear 8 jumbo (we mean oversize in a BIG way) or 24 standard-size muffin pans with butter.
In a medium bowl, whisk together the flour, ground pecans, baking powder, and salt.
In a separate, big bowl, whisk the eggs to break up the yolks. Still whisking with one hand, pour in the sugar with the other. Continue to whisk for a few minutes, until the eggs begin to pale in color. Whisk in the milk, vanilla, and melted butter.
Gradually add the dry ingredients to the wet, stirring gently with a wooden spoon. When there is still a little flour visible, gently stir in the blueberries, taking care not to break them up any more than is inevitable.
Scoop the batter up with a spoon and, using a rubber spatula, scrape the batter into the muffin cups, filling each almost to the top. You may want to wipe any excess topping off the pan so you won’t have to scrub burnt sugar from the tin after baking.
If using the crumb topping, sprinkle the topping evenly over the muffins. If not using the crumb topping, sprinkle with additional pecans.