Set your oven to 350°F (175°C). Grease a 9×5-inch loaf pan and dust it lightly with flour, or line it with parchment paper to make removing the loaf easier.

In a large mixing bowl, stir together the lemon cake mix, instant pudding mix, and all-purpose flour until evenly combined.

Crack in the eggs and add the vegetable oil, ½ cup of milk or water, sour cream, lemon juice, and lemon zest if using. Blend everything together with a hand or stand mixer until the batter is smooth and creamy. The consistency should be thick but pour able. If needed, mix in a little extra milk to loosen it up.

Pour the batter into the loaf pan and tap it gently on the counter to release any trapped air bubbles. Place it in the oven and bake for 45 to 50 minutes, or until a toothpick inserted in the center comes out clean.

Let the baked loaf rest in the pan for about 10 to 15 minutes. Then carefully transfer it to a wire rack and allow it to cool completely before adding the glaze.

In a small bowl, whisk together powdered sugar, fresh lemon juice, and a splash of milk until the glaze is smooth. Adjust as needed more sugar for a thicker consistency, more juice for a thinner drizzle.

Once the loaf is fully cooled, drizzle the glaze over the top. Let it set for 10 to 15 minutes. Slice and enjoy the sweet, zesty lemon flavour.