1-First Step: Set up the double boiler Fill the bottom of a double boiler with 1 to 2 inches of water and bring it to a gentle simmer. If you do not have a double boiler, place a heatproof glass bowl over a pot of simmering water. The key here is gentle heat, not a rolling boil. Direct heat can scramble the eggs fast, and nobody wants lemony scrambled eggs.

2-Second Step: Whisk the base ingredients In the top pot or bowl, whisk together the egg yolks, granulated sugar, lemon zest, fresh lemon juice, and salt until everything looks blended. The mixture may seem thin at first, and that is perfectly normal. Keep whisking until the sugar starts to dissolve and the color looks pale and even.

3-Third Step: Cook the curd slowly Place the bowl over the simmering water and whisk constantly for about 10 minutes. Keep the heat steady and gentle. The mixture will slowly thicken into a texture that feels a lot like hollandaise sauce. You are aiming for about 170 degrees Fahrenheit, or until the curd coats the back of a spoon.

4-Fourth Step: Add the butter Once the curd has thickened, remove it from the heat. Add the butter pieces one at a time and whisk until each piece melts into the mixture. This is where the curd turns glossy, rich, and velvety. The butter also softens the tart edge and gives the spread that spoonable, dreamy texture.

5-Final Step: Chill and set Pour the warm Lemon Curd into a clean jar or bowl. Cover it with plastic wrap so the wrap touches the surface of the curd. This prevents a skin from forming on top while it cools. Then refrigerate it until fully chilled and thicker.