Instructions

• Preheat the oven to 350°F. Spray the sides and bottom of two 9 x 5 x 3-inch loaf pans with nonstick cooking spray, line the bottoms with parchment paper, then spray the parchment.
• In a medium bowl, sift together 1-1/2 cups cake flour, 1-1/2 cups all-purpose flour, 2 teaspoons baking powder, 1/4 teaspoon baking soda, and 1 teaspoon salt; set aside.
• In a food processor, combine 2-1/4 cups sugar, 8 large room-temperature eggs, 1/4 cup grated lemon zest, and 1/4 cup fresh lemon juice. Pulse just until combined.
• With the food processor running, drizzle in 2 cups melted and cooled unsalted butter through the feed tube until incorporated. Add 1/2 cup room-temperature sour cream and 2 teaspoons vanilla extract, and pulse until just combined. Transfer the batter to a large mixing bowl.
• Add the sifted dry ingredients to the batter in three additions (one third at a time), folding gently with a spatula after each addition until just combined. Do not overmix.
• Divide the batter evenly between the two prepared loaf pans and smooth the tops. Bake on the center oven rack at 350°F for 20 minutes. After 20 minutes, rotate the pans, reduce the oven temperature to 325°F, and continue baking for 30 to 35 minutes more, or until a toothpick inserted into the centers comes out clean.
• Let the loaves cool in the pans for 15 minutes. While they cool, make the lemon syrup: in a small saucepan over medium heat, combine 1/3 cup fresh lemon juice and 1/3 cup sugar. Heat, stirring, until the sugar is completely dissolved, then continue to cook for 3 more minutes. Remove from heat and set aside.
• After 15 minutes, invert the loaves onto a parchment-lined half sheet pan. Use a toothpick or skewer to poke holes across the tops and sides of each loaf. Brush the tops and sides of the warm loaves with the lemon syrup, allow the syrup to soak in, then brush again to use most of the syrup. Let the cakes cool completely on the pan (at least 30 minutes).
• To make the lemon glaze, place 2 cups sifted powdered sugar in a small bowl and whisk in 4 tablespoons fresh lemon juice. The glaze should be thick but pourable; if it is too stiff, add up to 2 more tablespoons lemon juice a little at a time. If it becomes too thin, whisk in small amounts of additional powdered sugar until you reach the right consistency.
• Pour or spoon the glaze over the top of each cooled loaf, letting it drip down the sides. Allow the glaze to harden about 15 minutes before serving.
• Storage: the unglazed, syrup-soaked loaves can be wrapped in two layers of plastic wrap and frozen for up to 6 weeks. Glazed loaves, wrapped tightly in plastic wrap, will keep at room temperature for up to 3 days.