Preheat oven to 350 degrees Fahrenheit. Generously grease and lightly flour a nonstick bundt cake pan.
Using an electric mixer, beat the 1 (13.25-ounce) box lemon cake mix, 1 (3.4 ounce) instant lemon pudding mix dry, 1 cup sour cream, 4 large eggs, ½ cup vegetable oil, 1 teaspoon lemon zest, 4 tablespoons lemon juice, ½ teaspoon lemon extract, and ¼ cup water until just combined. Do not over-mix.
Pour the mixture and spread evenly in the bundt cake pan. Bake for 45-50 minutes. Let the cake cool for 10 minutes and then invert the cake onto a cake stand or plate.
In a small bowl whisk together ⅓ cup lemon juice juice and ⅓ cup granulated sugar. Brush this mixture generously over the cake being slow to allow it to soak in. Do this while it is still pretty warm and then let the cake cool completely before frosting.
Frosting
In a large bowl, whisk the¾ cup softened butter with 1 ½ teaspoons lemon zest on medium-high speed until very fluffy.
Mix in 1 cup of the 3 cups powdered sugar, 1 tablespoon lemon juice, 1 tablespoon heavy cream, ½ teaspoon vanilla extract, and 1 teaspoon lemon extract. Add the remaining powdered sugar, then whisk mixture until very fluffy (about 5 minutes).
Pipe or spread the frosting over the cake and enjoy!