French Lemon Cream Tart

Filling
1 cup sugar
Grated zest of 3 lemons
4 large eggs
3/4 c fresh lemon juice (from 4-5 lemons)
2 sticks plus 5 tbsp butter (10 1/2 ounces) unsalted butter, cut into tablespoon size pieces, at room temperature.

To make the filling

1. Have a 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.
   
2. Put the sugar and zest in a large heatproof bowl (Use a metal bowl, otherwise you'll be standing there forever.) 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.
   
3. 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 F. As you whisk (you 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 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 may take as long as 10 minutes.
   
4. As soon as it reaches 180F, 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 F, about 10 minutes.
   
5. 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 bend 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.
   
6. Pour the cream into a container, press a piece of plastic wrap (I just put mine in a tupperware container with no plastic wrap and it was fine.) against the surface to create an airtight seal and refrigerate at least 4 hours, or overnight. (The cream will keep in the fridge for 4 days or, tightly sealed, in the freezer for up to 2 months; thaw it overnight in the refrigerator.)
   
7. When you are ready to assemble the tart, just whisk the cream to loosen it and spoon it into the tart shell. Serve the tart, or refrigerate until needed.

Crust
Use Dorie Greenspan's Sweet Tart Dough

Serving: The tart should be served cold, because it is a particular pleasure to have the cold cream melt in your mouth.

Storing: While you can make the lemon cream ahead (it will keep in the frige for 4 days and in the freezer for up to 2 months), once the tart is constructed, it’s best to eat it the day it is made.

Notes: To recap, the recipe calls for the sugar, lemon zest, lemon juice and eggs to be mixed together in a bowl. The bowl is put over a saucepan with a few inches of boiling water and you whisk, whisk, whisk until the mixture thickens enough for the whisk to leave tracks, then you keep whisking until the cream measures 180 F on a candy or instant-read thermometer. To finish the cream, you pour it into a blender and cool it slightly before you whir in room-temperature butter -- but that's not the problemmatic part.

So here's what I did over the weekend -- I got bold! To make my double boiler, I used a soup pot and I filled it about 2/3 full of water, which I brought to a boil. I then put the bowl (a metal bowl) with all the ingredients over the steaming soup pot (making sure that the bottom of the bowl wasn't touching the boiling water) and whisked like mad. With so much heat under the bowl, the cream came up to 180 F in under 10 minutes (in fact, the first time I did it, it took 4 minutes and 39 seconds; the second time, it took almost 7 minutes -- different bowl, different pot, different stove).

Of course, if you're going to supercharge the power under the bowl, you've got to be vigilant -- you can't take your eyes off the cream; energetic -- you can't stop whisking, even for a few seconds; and nimble -- as soon as the cream shows the slightest signs of thickening, measure the temperature and make sure to remove the bowl from the heat immediately the instant you hit 180 F.

A couple of other re-thinks: If your lemon zest was very finely grated (I use a Microplane grater/zester), then you don't need to strain the cream -- just quickly scrape the hot cream from the bowl into the blender. And, while you shouldn't add the butter to the cream while it's still very hot (if you do, then the butter will melt, as it does in a lemon curd, and you won't get the great texture that sets this cream apart), you don't really need to measure the cream's temperature before you butterize it -- if you leave the cream in the blender for 8 to 10 minutes, it will be just the right temperature for blending in the butter.