Tartine Bakery's Lemon Cream

Directions

1. Pour water to a depth of about 2 inches into a saucepan, place over medium heat, and bring to a simmer.
2. Combine the lemon juice, whole eggs, yolk, sugar, and salt in a stainless steel bowl that will rest securely in the rim of a saucepan over, not touching, the water. (Never let the egg yolks and sugar sit together for more than a moment without stirring; the sugar will cook the yolks and turn them granular.) Place the bowl over the saucepan and continue to whisk until the mixture becomes very thick and registers 180° F on a thermometer. This will take 10 to 12 minutes. If you don't have or trust your thermometer, don't worry. It should thicken to the point that your whisk leaves a trail through the curd.
3. Remove the bowl from over the water and let cool to 140° F, stirring from time to time to release the heat.
4. Meanwhile, cut butter into 1-tablespoon (15-ml) pieces. When the cream is ready, leave it in the bowl if using an immersion blender, or pour it into a countertop blender. With the blender running, add the butter 1 tablespoon at a time, blending after each addition until incorporated before adding the next piece. The cream will be pale yellow and opaque and quite thick.
5. You can use the cream immediately, or pour it into a storage container with a tight-fitting lid and refrigerate for up to 5 days. To use after refrigeration, if necessary, gently heat in a stainless steel bowl set over simmering water until it has softened, whisking constantly.