• Preheat the oven to 375°F. Grease the cups of 1 standard (or 2 mini) muffin tin(s) (Do not use paper muffin cups/liners)

For the topping:

• In a medium bowl, combine the flour, oats, sugars, cinnamon, nutmeg and salt.
  60 g flour, 20 g old fashioned oats, 25 g sugar, 25 g brown sugar, 1 tsp cinnamon, 1/4 tsp nutmeg, 1/8 tsp salt
• Add the butter and cut into the dry mixture using a fork or pastry cutter until it resembles coarse crumbs with pieces no larger than a pea.
  56 g unsalted butter
• If you are using the pecans, stir them into the crumb mixture just to evenly distribute them. Set aside while preparing the muffin batter.
  28 g pecans

For the muffins:

• In large bowl, combine the flour, baking soda, baking powder, salt, cinnamon, and nutmeg. Set aside.
  180 g flour, 1 teaspoon baking soda, 1 teaspoon baking powder, 3/4 tsp salt, 1 tsp cinnamon, 1/4 tsp nutmeg
• In another medium bowl, combine the mashed bananas, sugars, egg and melted butter and mix until uniformly incorporated.
  390 g ripe bananas, 100 g sugar, 55 g brown sugar, 1 egg, 75 g unsalted butter
• Stir the wet ingredient mixture into the dry ingredients mixture just until moistened with no visible streaks or pockets of dry ingredients.
• Fill cups of your prepared muffin tin(s) two-thirds full. Using your hands, sprinkle the crumb topping mixture over the muffin batter distributing it evenly across all of the muffins. On a standard muffin you'll use about 1 1/2 to 2 tbsp of the crumb mixture on each muffin, on a mini muffin tin you'll use about 1 1/2 to 2 tsp of the crumb mixture on each muffin.
• Bake in the preheated oven for 5 minutes (or 2 minutes for mini muffins). Without opening the oven door, lower the temperature to 350°F and bake for an additional 12-14 minutes (8-10 minutes for mini muffins) or until a toothpick inserted in the center of a muffin shows just a few moist crumbs (~200-205°F on an instant read thermometer). Cool in the pan 10 minutes before removing to a wire rack to cool completely