1-First Step: Set up your double boiler Fill the bottom of a double boiler with 1 to 2 inches of water and bring it to a simmer over high heat. Once it starts gently bubbling, reduce the heat to low so the water stays at a steady simmer. If you do not have a double boiler, a heatproof glass bowl set over a pot works well too.

2-Second Step: Mix the base ingredients In the top part of the double boiler, whisk together the 4 large egg yolks, 2/3 cup granulated sugar, 1 tablespoon lemon zest, 1/3 cup fresh lemon juice, and 1/8 teaspoon salt. Whisk until the mixture looks well blended and the sugar starts dissolving.

3-Third Step: Cook slowly while whisking Set the top bowl over the simmering water and whisk constantly for about 10 minutes. Keep the mixture moving across the bottom and sides of the bowl so it heats evenly. The curd should slowly thicken and coat the whisk or the back of a spoon.

4-Fourth Step: Add the butter Remove the bowl from the heat once the curd has thickened and reached the right temperature. Add the 6 tablespoons of softened butter, a piece at a time, whisking until each piece melts completely before adding the next. This helps the curd turn glossy and rich.

5-Fifth Step: Strain and chill Pour the curd into a jar or bowl. If you want an extra-smooth finish, you can strain it through a fine mesh sieve, though the base recipe can be smooth enough without that extra step. Cover the surface directly with plastic wrap so a skin does not form on top. Refrigerate the curd until it thickens fully. This can take a few hours, and the full total time including cooling is about 1 hour 15 minutes. Once chilled, it should be thick enough to spread, pipe, or spoon.

6-Final Step: Serve and enjoy Your lemon curd is now ready to use. Spoon it onto toast, layer it in parfaits, fill tart shells, or serve it beside scones for a brunch spread that looks straight out of a bakery case. One batch yields about 1 to 1.5 cups, which is plenty for several servings.