Brown Butter Walnut Banana Bread

Preheat the oven to 350 degrees F. Grease a 9x5-inch loaf pan with butter and line the bottom and two long sides with a strip of parchment paper, leaving a slight overhang for easy removal.

Place the 1/2 cup of butter in a light-colored saucepan over medium heat. Swirl occasionally as it melts, foams, and then begins to turn golden. Watch closely once the foam subsides. When the milk solids at the bottom turn a deep amber color and the butter smells nutty and toasty (about 5 to 7 minutes), immediately pour it into a large heatproof mixing bowl. Scrape every last brown bit from the pan. Let it cool for about 10 minutes.

While the butter cools, spread the walnut halves on a small sheet pan and toast them in the oven for 7 to 8 minutes, tossing halfway through, until fragrant and a shade darker. Let them cool, then roughly chop.

Mash the bananas with a fork in a separate bowl. A few small lumps are fine and actually preferred for pockets of banana flavor throughout the loaf.

Whisk the dark brown sugar into the cooled brown butter until smooth and glossy. Add the whole egg, then the egg yolk, whisking well after each. Stir in the vanilla extract and the mashed bananas.

In a medium bowl, whisk together the flour, baking soda, salt, cinnamon, and nutmeg.

Add half of the dry ingredients to the banana mixture and fold gently with a rubber spatula until just barely combined. Fold in the sour cream, then add the remaining dry ingredients and fold until no streaks of flour remain. Do not overmix.

Fold in the chopped toasted walnuts, reserving about 2 tablespoons for the top.

Pour the batter into the prepared loaf pan and smooth the top with a spatula. Scatter the reserved walnuts over the surface. Brush the top lightly with the melted butter and sprinkle with the turbinado sugar.

Bake on the center rack for 50 to 60 minutes, rotating the pan halfway through. The bread is done when a toothpick inserted into the center comes out with just a few moist crumbs clinging to it, and the top is deeply golden brown.

Let the loaf cool in the pan on a wire rack for 15 minutes, then use the parchment overhang to lift it out. Cool for at least 30 minutes more before slicing. The texture improves dramatically if you can wait a full hour.