1 cup sugar
Finely grated zest of 3 lemons
4 large eggs
1/2 cup fresh lemon juice (from 4-5 lemons)
2 sticks plus 5 tablespoons (10-1/2 ounces)
unsalted butter, cut into tablespoon-size
pieces, at room temperature
Getting Ready: Have an instant-read thermometer, a strainer and a blender (first choice) or food processor at hand. Bring a few inches of water to a simmer in a saucepan.
Put the sugar and zest in a large heatproof bowl that can be set over the pan of simmering water. Off the heat, rub the sugar and zest together between your fingers until the sugar is moist, grainy and very aromatic. Whisk in the eggs, followed by the lemon juice.
Set the bowl over the pan, and start stirring with the whisk as soon as the mixture feels tepid to the touch. Cook the lemon cream until it reaches 180 degrees F. As you whisk—you must whisk constantly to keep the eggs from scrambling—you'll see that the cream will start out light and foamy, then the bubbles will get bigger, and then, as it gets closer to 180 degrees F, it will start to thicken and the whisk will leave tracks. Heads up at this point—the tracks mean the cream is almost ready. Don't stop whisking or checking the temperature, and have patience—depending on how much heat you're giving the cream, getting to temp can take as long as 10 minutes.
As soon as it reaches 180 degrees F, remove the cream from the heat and strain it into the container of the blender (or food processor); discard the zest. Let the cream stand, stirring occasionally, until it cools to 140 degrees F, about 10 minutes.
Turn the blender to high (or turn on the processor) and, with the machine going, add the butter about 5 pieces at a time. Scrape down the sides of the container as needed as you incorporate the butter. Once the butter is in, keep the machine going—to get the perfect light, airy texture of lemon-cream dreams, you must continue to blend the cream for another 3 minutes. If your machine protests and gets a bit too hot, work in 1-minute intervals, giving the machine a little rest between beats.
Pour the cream into a container, press a piece of plastic wrap against the surface to create an airtight seal and refrigerate for at least 4 hours or overnight. (The cream will keep in the fridge for 4 days and, or tightly sealed, in the freezer for up to 2 months; thaw it overnight in the refrigerator.)