Heat the oven to 350°F (175°C). Generously grease a 10- to 12-cup Bundt pan, including the center tube and decorative grooves, then dust it lightly with flour.

Whisk the lemon cake mix and instant lemon pudding mix together. Add the eggs, sour cream, oil, water, lemon juice, and optional lemon zest, then beat with an electric mixer on medium speed for about 2 minutes, until smooth and thick.

Pour the batter into the prepared pan and smooth the top. Bake for 45 to 55 minutes, or until a skewer inserted into the thickest part comes out clean or with a few moist crumbs.

Cool the cake in the pan for about 15 minutes. Carefully loosen the edges, invert the cake onto a rack, and cool completely for at least 30 minutes.

Whisk the powdered sugar and lemon juice together for the glaze, adding lemon juice a few drops at a time until thick but pourable. Drizzle it over the cooled cake and let it set for 10 to 15 minutes before slicing.