A high proportion of lemon juice gives curd its intense flavor. As an acid, the juice also prevents the yolks from curdling when heated (unlike when making pastry cream, which requires the extra step of tempering). You can substitute an equal amount of juice from other citrus, such as lime, grapefruit, or blood orange.

Ingredients

　　2 whole eggs plus 8 egg yolks 1 cup sugar

　　2/3 cup fresh lemon juice (about 6 lemons)

　　2 tablespoons unsalted butter, cut into small pieces, room temperature

　　Combine whole eggs and yolks, sugar, and lemon juice in a heatproof bowl set over a pan of simmering water. Cook, whisking constantly, until mixture is thick enough to coat the back of a spoon. Remove from heat. Add butter, a few pieces at a time, whisking until smooth after each addition. Strain through a fine sieve into another bowl, and cover with parchment paper or plastic wrap, pressing it directly on surface to prevent a skin from forming. Refrigerate until chilled and firm, at least 2 hours (or up to 2 days).

　　Martha Stewart's Cupcakes