Instructions

• Preheat the oven to 350 degrees F. Spray the sides and bottom of two 9-by-5-by-3-inch loaf pans with nonstick cooking spray, line the bottom of each pan with parchment paper, and spray the parchment.
• Sift the cake flour, all-purpose flour, baking powder, baking soda, and salt together into a medium bowl and set aside.
• In a food processor, combine the sugar, eggs (room temperature), grated lemon zest, and lemon juice; pulse until combined.
• With the food processor motor running, drizzle in the melted and cooled butter through the feed tube. Add the sour cream (room temperature) and vanilla extract and pulse until just combined. Transfer the batter to a large bowl.
• Add the sifted flour mixture to the batter in three additions (one third at a time), folding gently after each addition until just combined. Do not overmix.
• Divide the batter evenly between the two prepared loaf pans and smooth the tops. Place the pans in the center of the oven and bake for 20 minutes.
• After 20 minutes, rotate the pans, reduce the oven temperature to 325 degrees F, and continue baking for another 30 to 35 minutes, or until a toothpick inserted into the center of each loaf comes out clean.
• Remove the pans from the oven and let the loaves cool in the pans for 15 minutes.
• While the loaves are cooling, 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.
• Line a half-sheet pan with parchment paper. Invert the loaves onto the sheet pan. Use a toothpick to poke holes in the tops and sides of the loaves.
• Brush the tops and sides of the loaves with the warm lemon syrup. Allow the syrup to soak in, then brush again. Let the cakes cool completely, at least 30 minutes.
• (Optional) To make the lemon glaze, in a small bowl whisk together the sifted powdered sugar and 4 tablespoons fresh lemon juice until the mixture is thick but pourable. If it is too stiff, add up to 2 more tablespoons lemon juice, whisking until you reach the desired consistency; if it becomes too thin, add a little more powdered sugar. Pour the glaze over the top of each loaf and let it drip down the sides. Let the glaze harden about 15 minutes before serving.
• Storage: The soaked but unglazed loaves, wrapped in two layers of plastic wrap, can be frozen for up to 6 weeks. Glazed loaves, wrapped tightly in plastic wrap, will keep at room temperature for up to 3 days.