Preheat the oven to 350 degrees F. Butter the sides and bottom of a 9 x 5-inch loaf pan. Dust with flour and set aside.
In a medium bowl, combine the flours, baking powder, baking soda, and salt. Whisk and set aside. In the bowl of an electric mixer fitted with a paddle attachment, combine the sugar, eggs, lemon zest and lemon juice. With the mixer on low speed, mix in the melted butter. Add half of the dry ingredients just until incorporated. Beat in the sour cream and vanilla until combined. Mix in the remaining dry ingredient just until incorporated.
Transfer the batter to the prepared pan. Bake 20 minutes, then rotate pan and reduce the oven temperature to 325 degrees F. Continue baking 30 to 35 minutes or until a toothpick inserted in the center comes out clean. Let cool in the pan for at least 15 minutes.
For the glaze:
When the cake is completely cool, combine the confectioners' sugar and lemon juice in a small bowl and whisk to blend until smooth. Drizzle the glaze over the top of the loaf. Let stand briefly until the glaze hardens. Slice and serve.
Notes
For the best lemon flavor: Use fresh lemon zest and juice. Bottled juice won’t give the same bright citrus taste.
Don’t overmix the batter: Once the flour is added, mix just until it disappears to keep the loaf tender.
Glaze tip: Let the loaf cool completely before adding the glaze so it sets nicely on top instead of melting into the cake.
Storage: Keep the loaf covered at room temperature for up to 3 days or refrigerate for up to 5 days.
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