Preheat oven to 350F and grease two 8x4" loaf pans well.
In the bowl of a stand mixer fitted with the paddle attachment (or in a large mixing bowl with an electric hand mixer), combine cake mix, flour, dry lemon pudding mix, oil, water, sour cream, eggs, and lemon zest. Mix on low speed for about 30 seconds, then scrape down the sides of the bowl and mix on high speed for about 2 minutes.
Pour batter into prepared loaf pans and bake for about 32-36 minutes, or until a toothpick inserted in the center of the loaves comes out clean.
Remove from oven and allow to cool completely.
Once cool, turn loaves out onto a plate for serving.
Prepare glaze by combining powdered sugar and 3 tablespoons of lemon juice in a small bowl. Whisk together until smooth.
If needed, add up to 1 tablespoon more of lemon juice, a little bit at a time, until glaze can be easily drizzled over the cakes.
Drizzle glaze evenly over the loaf cakes. Allow glaze to set to a satiny finish, then slice and serve.
Notes
Although the glaze is optional, we like to add it for an extra burst of flavor.
Unglazed loaf cakes freeze well. Simply cool completely, then wrap well with plastic wrap and freeze. Once thawed out, you can prepare the glaze and drizzle over the cakes.
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