Make the Lemon Curd:

1. Start by filling the bottom pot of a double boiler with 1-2 inches of water and bring to a simmer. If you don't have a double boiler, fill a small pot with 1-2 inches of water and bring to a simmer while you prep the lemon curd.
2. To the top pot of a double boiler or a large glass bowl, add the sugar and lemon zest. Rub with your hands until the mixture is fragrant and combined.
3. Add the egg yolks and whisk vigorously for 1-2 minutes, or until the mixture lightens in color.
4. Slowly pour the lemon juice into the egg yolk mixture while whisking constantly.
5. Place the bowl or top pot of the double boiler on top of the pot of simmering water. Whisk constantly until the curd thickens to a sauce consistency, about 10-15 minutes. Keep in mind the curd will continue to thicken as it cools.
6. Once thickened, immediately take the curd off the heat and add the butter. Whisk until the butter melts and combines with the curd.
7. Strain the curd through a fine mesh sieve into a large shallow bowl.
8. Cover the curd with plastic wrap, pressing the plastic directly against the surface of the curd to prevent it from forming a skin.
9. Refrigerate the lemon curd while you make the cupcakes, or for up to 2 days.

Make the Lemon Cupcakes:

1. Preheat oven to 350°F (177°C). Line 2 mini cupcake pans with 40 mini cupcake liners. Set aside.
2. Add the sugar and lemon zest to a food processor. Pulse until the lemon zest breaks down into small pieces.
3. Sift the lemon sugar, cake flour, baking powder, baking soda, and salt into the bowl of a stand mixer. Mix  using a paddle attachment on low speed for 30 seconds.
4. Add the butter to the dry ingredients. Beat on low speed until it breaks down into fine crumbs that resemble sand.
5. To a medium bowl or a large liquid measuring cup, add the buttermilk, oil, egg, and egg white. Whisk until combined.
6. With the mixer running on low speed, slowly stream the wet ingredients into the dry ingredients. If at any point the batter looks lumpy or curdled, stop adding more liquid, increase speed to medium, and allow the batter to beat together for 20-30 seconds until it smooths out. Scrape down the sides and bottom of the bowl as needed, and continue streaming in the wet ingredients until fully incorporated into the batter. The finished batter should be thin and smooth.
7. Divide the batter between the cupcake liners, filling 2/3-3/4 of the way full. I highly recommend weighing the amount of batter in each tin- 15g of batter each produces cupcakes that are all even and perfectly tall.
8. Bake for 10-14 minutes, or until a toothpick comes out clean or with a few moist (not wet) crumbs.
9. Allow the cupcakes to cool inside the pans for 5 minutes, then remove from the pans and set over a wire rack to cool completely to room temperature before filling and frosting.

Make the Whipped Cream & Assemble:

1. Add the cream cheese and sugar to the bowl of a stand mixer fitted with a whisk attachment. Whip on high speed for 3 minutes, scraping down the bottom and sides of the bowl as needed.
2. Slowly pour the lemon juice into the cream cheese mixture with the mixer running on low speed.
3. Keep the mixer running at low speed and slowly stream in the heavy cream. Once all of the cream has been added, increase the speed to high and continue whipping until the frosting thickens to a stiff consistency.
4. Cover with plastic wrap and refrigerate while you fill the cupcakes.
5. Use a small knife or round piping tip to cut a hole in the center of each cupcake. Discard or snack on the cake cores.
6. Fill each cupcake with lemon curd using a teaspoon or by piping it inside.
7. Top each cupcake with frosting, either by spreading it on with a knife or piping it on. For the pictured cupcakes, I used 18-inch piping bags and piping tips Ateco #8 and Ateco #869.
8. Serve cupcakes immediately, or store in an airtight container in the refrigerator for up to 2 days. Bring cupcakes to room temperature before enjoying for the optimal soft, moist texture.