Prep. Heat oven to 350°F (177°C). Grease a 9×5-inch loaf pan and line with a parchment sling for easy lift-out.

Brown the butter (5–10 min). Add ½ cup (113 g) butter to a light-colored saucepan over medium heat. Stir continuously as it melts, foams, and then the milk solids turn deep amber. When it smells nutty and the sizzling quiets, pull from heat. Pour into a large bowl, scraping in all the browned bits. Cool 5 minutes.

Whisk with sugar. Whisk in 1 cup brown sugar until the mixture looks glossy and cohesive.

Bananas in. Mash bananas very well (no big chunks) and whisk them into the bowl.

Add egg + vanilla. Whisk in 1 egg and 1 tsp vanilla until smooth.

Dry ingredients. In a separate bowl (or right on top), add 2 cups flour, 1 tsp cinnamon, 1 ½ tsp baking powder, ½ tsp fine salt. Fold with a spatula until just combined—thick but scoopable.

Chocolate chips. Fold in 1 cup semi-sweet chips.

Pan it. Smooth batter into the prepared pan and tap once on the counter to release air.

Make the crumble. Stir together 3 tbsp melted butter, ½ cup brown sugar, ½ cup flour, 1 tsp cinnamon until sandy with clumps (think wet sand that forms pea-to-almond-size clusters). Fold in ¼ cup mini chips.

Top it. Crumble evenly over the batter, lightly pressing so it adheres.

Bake. Bake at 350°F for 65–75 minutes. At 65 minutes, check: a toothpick in the center should come out with a few moist crumbs (no wet batter). If the top is browning fast, tent loosely with foil at the 45–50 minute mark.

Cool. Let the loaf cool in the pan 20 minutes, then lift out to a rack and cool at least 45–60 minutes before slicing.