Preheat your oven to 350°F (175°C). Prepare two small loaf pans by coating them with non-stick spray.

In a large mixing bowl, combine the vanilla pound cake mix with cold water, melted unsalted butter, a large egg, fresh key lime juice, and key lime zest. Optional food coloring can be added. Use a hand mixer on medium speed, mixing just until blended.

Carefully divide the batter evenly between the two prepared loaf pans. Gently tap the pans against the counter to eliminate any air bubbles.

Transfer the pans to the oven and bake for 30–35 minutes. Cakes are ready when they turn light golden and a toothpick comes out clean.

Allow the cakes to cool in the pans for about 10 minutes. Then place them upright on a wire rack to cool completely.

Whisk together the powdered sugar, fresh key lime juice, and additional zest in a small bowl until smooth for the glaze.

Once the cakes are cooled, pour the glaze generously over the top of each loaf, allowing it to drizzle down the sides.

Slice the cake and serve, optionally with whipped cream and a lime wedge.