Combine Topping: In a medium mixing bowl, add the flour, sugar, cinnamon, and melted butter. Mix with a spoon until the mixture forms coarse, well-combined crumbs. Set aside.
Make the Muffin Batter
Prep and Mix Wet Ingredients: Preheat your oven to 180°C (350°F) and line a 12-cup muffin pan with paper liners.
Incorporate Dry Ingredients: Add the flour, baking powder, and baking soda, and mix gently until almost combined.
Add Chocolate Chips: Add the chocolate chips and fold gently with a spatula until just combined.
Fill Tins: Use an ice cream scoop or large spoon to fill each muffin cup about two-thirds full to allow room for rising.
Add Topping and Bake
Top with Streusel: Add about 1 tablespoon of the streusel topping to each muffin, gently pressing the crumbs onto the batter so they adhere securely.
Bake: Bake in a preheated 180°C (350°F) oven for 18 to 20 minutes, or until a toothpick inserted into the center comes out clean. Let the muffins cool for at least 15 minutes before serving.
Notes
Room-Temperature Ingredients: Ensure your eggs are at room temperature so the batter emulsifies into a smooth mixture that bakes evenly.
Measure Flour Correctly: Fluff your flour with a spoon, scoop it into your measuring cup, and level it off with a knife to avoid packing too much flour.
Ripe Bananas: Use heavily speckled, ripe bananas for maximum sweetness, moisture, and easy mashing.
Do Not Overmix: Fold in the flour and chocolate chips just until combined to prevent developing excess gluten, which can make the muffins dense.
Secure the Streusel: Gently press the cinnamon streusel topping onto the muffin batter before baking so it adheres securely and stays crunchy.
Cooling: Let the muffins cool in the pan for 15 minutes before handling so they firm up and don't crumble apart.