Preheat the oven to 350°F.

In a large bowl, whisk to combine the flour, baking powder, salt, and baking soda.

In a large mixing bowl or the bowl of a stand mixer fitted with the paddle attachment, beat butter, sugar, and lemon zest on medium speed for about 3 minutes, until lightened, fluffy, and fragrant.

Add the eggs one at a time while mixing on medium speed, scraping the bowl down once or twice. Beat in the vanilla.

In a liquid measuring cup, whisk to combine the milk, sour cream, and lemon juice.

Add one-third of the flour mixture, mixing on low speed until combined. Add half of the milk mixture, and mix until combined. Repeat, alternating with the rest of the flour and milk mixtures.

Butter and flour a 10- to 12-cup Bundt pan or spray with baking spray with flour.

Pour the cake batter into the pan and tap gently on the counter a few times to settle the batter.

Bake for 50 minutes or until golden brown and a toothpick inserted into the center comes out with a few moist crumbs.

Let cool in the pan for 20 minutes. Turn onto a cooling rack and let cool completely.

In a small bowl, whisk together the powdered sugar, 3 tablespoons lemon juice, butter, salt, and lemon zest, if using.

Add additional lemon juice, ½ teaspoonful at a time, until the icing is smooth, thick, and pourable. Pour over top of the cooled cake. Let sit until hardened.