Brown the butter

• Melt the butter in a saucepan over medium heat.
• Cook until the milk solids turn golden brown and smell nutty, then set aside to cool.

Make the brownie batter

• Melt the chocolate with the butter for the brownie batter.
• Whisk in the sugar, egg and vanilla, then fold in the flour, cocoa powder and salt until thick.

Make the banana bread batter

• Whisk the cooled brown butter with the brown sugar and granulated sugar.
• Beat in the eggs, mashed bananas, vanilla and sour cream.
• Fold in the flour, baking soda and salt until just combined.

Layer in the pan

• Spread half of the banana bread batter in the greased loaf pan.
• Make a shallow divot in the middle with a large spoon and spoon in the brownie batter, spreading it out.
• Cover with the remaining banana bread batter.

Bake

• Bake until golden and a skewer inserted near the edge comes out with moist crumbs.
• Let cool in the pan before slicing.

Serve

• Serve warm with a pat of butter and a sprinkle of flaky sea salt.