Heat oven to 350º. Butter the sides and bottoms of two standard 9-inch loaf pans. Line the bottoms with parchment and butter the parchment.

In a medium bowl, whisk together the flours, baking powder, baking soda and salt. Set aside. In the bowl of a stand mixer fitted with the paddle attachment, combine the sugar, eggs, lemon zest and lemon juice on low speed. With the mixer running, slowly pour in the melted butter. Add the sour cream and vanilla and continue mixing until combined. Gradually add the flour mixture and use a rubber spatula to gently fold it in, taking care not to overmix.

Divide the batter evenly between the prepared pans. Bake on the middle rack for 20 minutes, rotate the pans, reduce oven temperature to 325º and continue baking an additional 30-35 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool in the pans for 15 minutes.

Meanwhile, make the lemon syrup. Combine the lemon juice and sugar in a small saucepan over medium heat. Stir until the sugar is completely dissolved, then continue to cook about 3 more minutes. Remove from heat and set aside.

Remove the loaves from the pans and place on a parchment lined cookie sheet. Use a toothpick to poke holes in the tops and sides of the loaves. Brush with the lemon syrup, allow to soak in and brush again. Allow the cakes to cool completely (at least 30 minutes). If you’d like to freeze a loaf, this is the time to do it.

When the loaves are cool, prepare the lemon glaze. In a small bowl, whisk together the confectioners’ sugar and 4 tablespoons lemon juice. The glaze should be thick but pourable. Add more lemon juice if needed to reach desired consistency. Pour glaze over the top of each loaf and let it drip down the sides. Let the loaves sit for about 15 minutes, or until the glaze hardens, before serving. The glazed loaves, tightly wrapped in plastic, will keep for 3 days.