1. Preheat the oven to 325°F (165°C). Grease and flour a Bundt pan or a 9×13-inch baking dish.

2. In a large bowl, whisk together the yellow cake mix and lemon pudding mix until combined.

3. Add the oil, eggs, and 7UP soda. Beat with an electric mixer on medium speed for 2–3 minutes, until the batter is smooth and creamy.

4. Fold in the lemon zest (and vanilla if using).

5. Pour the batter into the prepared pan and smooth the top.

6. Bake for 45–50 minutes (Bundt) or until a toothpick inserted in the center comes out clean. If using 9×13, check at 35–40 minutes.

7. Cool the cake in the pan for 10 minutes, then invert onto a wire rack and cool completely.

8. For the glaze, whisk together powdered sugar, lemon juice, and 7UP until smooth. Drizzle over cooled cake.

9. Store leftovers in an airtight container at room temperature up to 3 days, refrigerate up to 5 days, or freeze up to 2 months.