Preheat the oven to 350°F. Butter and flour your Bundt pan.
Mix the eggs, egg yolks, vanilla, lemon juice, and the sourdough discard together in a medium bowl.
Mix the flour, sugar, lemon zest, baking powder, and salt in a stand mixer using the beater or paddle attachment on low speed. If you do not have a stand mixer a large bowl also works.
With the mixer running add the cubes of butter followed by the buttermilk.
Increase the speed to medium and allow the batter to fully mix, scraping the sides.
Slowly add the egg and sourdough mixture, continuing to scrape the sides.
Mix until fully combined.
Pour the batter into the prepared pan.
Bake until a toothpick or knife inserted into the center comes out clean, about 40 minutes.
Cool for 15 minutes in the pan. Transfer the cake onto a cooling rack (have the rack on top of a sheet pan or plate to catch any drips while glazing). Prepare the glaze and glaze while still slightly warm.