Grab a double boiler or place a heatproof bowl over a saucepan so its bottom doesn’t touch the water. Fill the top pot or the bowl with 2 inches of water and heat it on high. Once bubbling, turn the heat to low and let the water simmer.

Add egg, egg yolks, lemon juice, lemon zest, salt, and granulated sugar to the bowl or the top pot. Constantly whisk the mixture using a silicone whisk until incorporated.

Keep whisking over low heat as the curd thickens, resembling a thick soup or hollandaise sauce. Take the pan off the heat after 10 minutes or when it reaches 160°F or 71°C.

Cut 6 small cubes of butter and whisk it into the warm curd until it melts and folds in completely, yielding 1 cup of lemon curd.

Transfer the curd into a bowl or a jar and gently press a sheet of plastic wrap directly onto its surface. Refrigerate it for faster cooling and thickening.

Preheat your oven to 350°F or 177°C. Grease three 6” round cake pans, line them with parchment paper, and grease the paper again.

Mix the flour, salt, and baking powder together in a medium bowl. Set aside.

Toss ½ cup of unsalted butter and 1 cup of granulated sugar in a mixing bowl and beat them on medium-high for 1 minute using an electric stand or hand-held mixer with a whisk or paddle attachment.

Scrape down the bowl and add 1 ½ tablespoons of citrus zest, including orange, lime, and lemon zest. Continue beating the mixture on medium-high for 2 minutes until creamy.

Fold in pure vanilla extract and eggs on medium-high until combined. Scrape down the bowl and continue beating until incorporated (if needed).

Toss half of the dry ingredients (step 6), half of the citrus juice, and half of the whole milk into the bowl. Beat the mixture on low until mostly blended. Fold in the remaining flour mixture, citrus juice, and whole milk on low until incorporated. Whisk the mixture by hand several times to smooth it out, but a few small lumps are okay.

Pour the batter equally into the three prepared pans. Tap them on the counter to release any air pockets, and bake for 18-21 minutes. It’s ready if an inserted toothpick comes out clean.

Let the cakes cool on a wire rack for about half an hour while still sitting in the pans. Then, remove them from the pans and place them on a wire rack to completely cool.

Beat 6 ounces of cream cheese in a medium bowl on medium-high using a stand or hand-held mixer with a paddle and whisk attachment for around 1 minute until creamy. Scrape down the bowl and continue mixing until smooth (if needed).

Fold in ¾ cup of confectioners’ sugar and 1 ½ teaspoons of vanilla extract at medium speed until lump-free, around 2 to 3 minutes. Scrape down the bowl and stir up the bottom.

Slowly pour the cold cream into the bowl while beating on low with a whisk attachment. Once you’ve poured all the cream, crank up the mixer to high speed and beat for 1 to 2 minutes until stiff peaks form. Keep whipping if the frosting looks soupy. If it’s curdled or chunky, whisk in about 1 tablespoon of heavy cream by hand to smooth it out.

Mix 1 cup of the freshly made whipped frosting with 3 tablespoons of lemon curd in a separate bowl.

Use a long serrated knife to even out the cakes if they are domed. Put one layer on a serving plate, a cake turntable, or a cake stand, and evenly top it with half of the lemon curd filling. Continue with the 2nd cake layer and the remaining curd.

Put the final layer on and cover it with a super thin whipped frosting layer using an icing spatula or a bench scraper. Refrigerate it for around half an hour without covering it.

Remove the cake from the fridge and frost it evenly with the remaining cream cheese frosting. Refrigerate the frosted, uncovered cake for another 30 minutes.

Remove it from the refrigerator, slice it with a clean, sharp knife, and dig in!