• Begin by preheating your oven to 400 degrees Fahrenheit (204 degrees Celsius).
• Lightly grease 6 wells in each of two standard 12-cup muffin pans, or line with cupcake liners and grease. Set aside.

Make the Crumb Topping

• Put all the crumb topping ingredients in a medium bowl.
• Use a fork, pastry cutter or your hands to cut the butter into the dry ingredients until the mixture forms large crumbs.

Make the Muffin Batter

• In a medium bowl, combine the flour, baking soda, baking powder, sea salt and cinnamon, set aside.
• In a large bowl, mash bananas.
• Add melted butter and stir to combine.
• Then, add the eggs, vanilla, light brown sugar and granulated sugar and stir to combine.
• Add the dry ingredient mixture and stir until the flour is fully incorporated.

Assemble, Bake & Cool

• Place about ¼ cup of batter into 12 wells of the prepared muffin pans (filled about ¾ full), spaced out.
• Put about 1 to 2 Tablespoons of crumb topping on the top of each muffin and gently press it into the batter. Do not let the crumb topping overflow from the muffins because it will burn on the pan.
• Bake in the preheated oven for 12 to 15 minutes, or until the muffins are domed, the tops look set and a toothpick inserted into center of a muffin comes out clean.
• Immediately use a spoon or sharp knife to release any crumb topping stuck to the top of the pan.
• Let the muffins cool for 15 minutes in the muffin pan before using a spoon or knife to lift them out of the pan and transfer them to a wire cooling rack to cool completely.