Preheat your oven to 325 degrees and generously spray a 10-inch bundt pan with non-stick spray. Set aside.
To a large bowl, cream together the sugar and butter with a hand mixer on medium until light and fluffy.
Beat in the lemon zest and vanilla, then the eggs, one at a time, beating until each egg is incorporated. Scrape down the sides of the bowl if needed.
To another medium bowl, whisk together the flour, lemon pudding mix, baking powder, and baking soda.
To a measuring cup, add the buttermilk then whisk in the lemon juice.
Add the dry ingredients and buttermilk to the butter-sugar mixture in multiple additions, alternating back & forth, starting and ending with the flour mixture and beating on medium speed. Scrape down the sides of the bowl as needed.
Pour the batter into the prepared bundt pan and bake for approximately 65 minutes or until a toothpick inserted into the center comes out clean.
Let cool for about 10 minutes then flip onto a wire rack to cool completely.
Cut & serve.
Store covered in plastic wrap or in an airtight container for 4-5 days at room temperature.Top with powdered sugar or lemon glaze.