Bananas past their prime take on an entirely new life in this dialed up rendition of traditional “Banana Nut Muffins”. Browned butter adds a naturally rich nutty flavor to batter that is flecked with hazelnuts. But the real star is the unexpected creamy chocolate hazelnut filling tucked inside.
Place a rack in the center of the oven set to 375°F. Line a 12-cup standard muffin tin with paper liners.
Melt the butter in a small saucepan over medium heat. Cook, stirring occasionally, scraping milk solids off the bottom and sides of the pan, until the milk solids turn golden brown and smell nutty, about 10 minutes. Pour the butter and brown bits into the mixing bowl and cool for 10 minutes.
Make crumb topping: Add the sugar, flour and butter to a small bowl and mix with fingers until crumbs form.
In a medium bowl, stir together flour, baking powder, baking soda, and salt. Reserve.
Using a stand or hand-held electric mixer, cream cooled brown butter and sugars for 1 to 2 minutes, until light and fluffy. Beat in eggs and vanilla. Mix in bananas. Add flour mixture in increments until just combined. Stir in hazelnuts.
Spoon a heaping tablespoon of batter into each muffin cups. Place a heaping teaspoon of hazelnut spread in the center of each. Top each with another heaping tablespoon of batter. Top each generously with crumb topping. Sprinkle tops with sea salt. Bake for 20 to 25 minutes, or until a cake tester inserted in center of one muffin comes out clean.
Remove muffin tin(s) to wire rack. Cool for 5 minutes before removing muffins