Lemon-Lemon Lemon Cream

Ingredients

• 1 cup sugar
• Finely grated zest of 3 lemons
• 4 large eggs
• 3/4 cup freshly squeezed lemon juice
• 2 sticks plus 5 tablespoons unsalted butter, at room temperature and cut into tablespoon-sized pieces
• 1 fully-baked 9-inch tart shell

Directions

1. Set yourself up with a thermometer, preferably instant-read, plus a strainer and either a blender, which is ideal, or a food processor. Bring a few inches of water to a simmer in a saucepan. Place the sugar and zest in a large metal bowl that will sit securely over the pan. Away from the heat, rub the sugar and zest together with your fingers until the sugar feels damp, gritty and fragrant. Whisk in the eggs, then whisk in the lemon juice.
2. Set the bowl over the simmering water, making sure the water is not touching the bowl. Once the mixture feels warm, begin whisking and continue without stopping so the eggs stay smooth. Cook the cream until it reaches 180 degrees F. It will begin pale and foamy, then the bubbles will grow larger, and as it nears 180 degrees F, the mixture will thicken enough for the whisk to leave visible lines. When you see those lines, stay close: keep whisking and keep checking the thermometer. Depending on the heat, this can take as long as 10 minutes.
3. The moment the cream reaches 180 degrees F, take it off the heat and pour it through the strainer into the blender or food processor, leaving the zest behind. Let it stand at room temperature, stirring now and then, until it comes down to 140 degrees F, about 10 minutes. Run the blender on high and, while it is running, add the butter about 5 pieces at a time. Stop to scrape the sides of the container whenever you need to. After all the butter has been added, continue blending for another 3 minutes to make the cream light and airy. If the motor seems to be getting too warm, blend in 1-minute bursts, letting it rest briefly between rounds.
4. Transfer the cream to a container, press plastic wrap directly onto the surface so it is sealed, and refrigerate for at least 4 hours or overnight. When you are ready to assemble the tart, whisk the cream just to loosen it, then spoon it into the tart shell. Serve the tart cold. The lemon cream can be made ahead and stored in the frige for 4 days or in the freezer for up to 2 months, but after the tart is assembled, it is best eaten the same day.