Onion Loaf

Ingredients

• 5 tablespoons unsalted butter
• 1.5 teaspoons neutral oil
• 1 medium yellow onion, chopped
• Kosher salt
• 1 small leek (white and light green parts), halved lengthwise and thinly sliced
• 2 cups whole-wheat flour
• 1 cup all-purpose flour
• 1.5 tablespoons onion powder
• 2.5 teaspoons baking powder
• ¼ teaspoon baking soda
• {=amount1/c} {=amount1/c|egg|eggs}
• 1 tablespoon light brown sugar
• ¾ cup buttermilk
• ¾ cup thinly sliced scallions (white and green parts)

Instructions

1. With a rack in the middle position, preheat the oven to 375°F.
2. In a small skillet over medium heat, melt 1 tablespoon of the butter with the neutral oil. Add the onion and ¾ teaspoon salt and cook, stirring occasionally, until the onion is translucent and starting to soften, about 3 minutes. Add the leek and cook, stirring occasionally, until softened, about 3 minutes longer. Scrape the mixture into a bowl and set aside to cool.
3. Return the skillet to medium heat and melt the remaining 4 tablespoons butter. Remove from the heat and pour about 1 tablespoon of the melted butter into a 10- to 11-inch oval gratin dish (preferably enameled cast iron). With a pastry brush, coat the inside of the dish with the butter and set aside. Reserve the remaining melted butter in the skillet.
4. In a large bowl, combine both flours, the onion powder, baking powder, baking soda, and 1¼ teaspoons salt and whisk together. In another large bowl, whisk together the eggs and brown sugar. Add the buttermilk to the egg mixture and whisk to combine. Add the dry mixture and, using a flexible spatula, fold and stir until nearly incorporated. Add the reserved melted butter and the scallions and continue to fold and stir until all the ingredients come together to form a lumpy dough. Knead a couple of times in the bowl, if necessary.
5. Scrape the dough into the prepared dish, shape into an 8-inch log, and spread the reserved onion mixture evenly over the top and sides, pressing into the dough to help it adhere.
6. Bake the loaf until it is firm to the touch on top, a toothpick inserted into the center comes out clean, and the onion mixture on the surface is browned with some crisp edges, 45 to 50 minutes, rotating halfway through. Let cool in the gratin dish for about 10 minutes, then transfer the bread to a wire rack to cool to room temperature. Slice with a serrated knife before serving.