Add the cream cheese to a large mixing bowl and mix on medium-high speed until smooth, 1-2 minutes.

Add in the egg and egg yolk and mix on medium speed until combined.

Then add in the lemon zest and half the powdered sugar, mixing on low then medium speed until all is combined. Then add the remaining powdered sugar and mix just until combined. Set aside.

Preheat the oven to 350 ℉ (175 ℃). Grease a 9-inch springform pan and line the bottom with parchment paper. Set aside.

In a small bowl, whisk together the all-purpose flour, baking powder, baking soda and salt. Then set aside the dry ingredients.

To a large bowl, add the sugar and lemon zest. Rub the lemon zest and sugar together with your fingertips to extract the most lemon flavor from the zest.

Then add in the softened butter. Cream the sugar and butter together with an electric mixer on high speed until fluffy, about 1-2 minutes.

Then add in the egg, egg yolk, and vanilla and mix on medium-high speed until smooth and pale in color, about 1-2 minutes. Scrape the sides of the bowl with a rubber spatula as needed.

Add the flour mixture and the buttermilk to the wet ingredients a little at a time, mixing on low speed until all is combined and the batter is smooth.

Pour the batter into the prepared baking pan and spread it evenly with a mini offset spatula. Then pour the cream cheese mixture over top and spread it evenly as well.

Bake the cake for 35-40 minutes, or until the center is shiny, has a jiggle still, and the edges are a light golden brown color.

Then let the cake cool in the pan on a wire rack for 45 minutes. Then transfer the cake to the fridge to cool for 2 hours.

While the cake cools, make the lemon curd. Add the lemon juice, lemon zest, egg yolks, sugar, and salt to small pot. Whisk everything together.

Heat the lemon mixture over medium low heat for 12-15 minutes, stirring frequently, until thick. It should coat the back of a spoon once thick enough.

Remove it from the heat and slowly whisk in the cold, cubbed butter.

Once all of the butter is melted in, transfer the lemon curd to a heat proof, medium bowl. Place plastic wrap on top of the curd, so it doesn't form a skin, and allow it to cool completely.

Once the cake has cooled, remove it from the springform pan and transfer it to a serving plate.

Pour the lemon curd over the top and spread it evenly with an offset spatula.

The cake is best served at room temperature, so if you're preparing the cake the day before and letting it chill in the fridge overnight, pull it out and let sit for an hour at room temperature, then pour the lemon curd over top and serve.