Brown the Butter: Place ½ cup of unsalted butter in a heavy-bottomed saucepan over medium heat. Stir constantly with a whisk or spatula until it turns golden brown and develops a nutty aroma. Remove from heat and let cool.

Mix the Wet Ingredients: Add 1 cup of light brown sugar to the cooled brown butter and whisk until smooth. Mash 3 overripe bananas and mix in with 1 large egg, ¼ cup of whole milk, and 1 teaspoon of vanilla extract.

Prepare the Dry Ingredients: In a separate bowl, sift together 2 cups of all-purpose flour, 1 ½ teaspoons of baking powder, and ¼ teaspoon of salt. Gently fold into the wet mixture.

Assemble the Batter with the Cinnamon Sugar Swirl: Grease a 9×5-inch loaf pan. Pour half of the batter into the pan, sprinkle with a mixture of ⅓ cup granulated sugar and 1 teaspoon cinnamon, then top with the remaining batter.

Add the Cinnamon Crumble Topping: Mix 3 tablespoons melted unsalted butter, ½ cup all-purpose flour, ½ cup light brown sugar, and ½ teaspoon cinnamon until crumbly. Sprinkle over the batter.

Bake the Banana Bread: Preheat oven to 350°F (175°C) and bake for 60–70 minutes. Check for doneness with a toothpick.

Cool and Apply the Optional Glaze: Let cool for 10 minutes in the pan, then transfer to a wire rack. If desired, mix ¼ cup powdered sugar with ½ tablespoon heavy whipping cream and drizzle over the cooled loaf.

Slice, Serve, and Enjoy: Let the bread rest for at least an hour before slicing. Serve at room temperature.