French Lemon Cream Tart

I found this recipe on chowhound and decided on a last minute change to Christmas dinner plans. I'm certainly glad I did as this cream tart is nothing short of delicious (granted I have a thing for lemon dishes). I didn't make the tart shell, because as usual that would've been just a step too far (and I didn't want to run to the grocery store on Christmas Eve to buy more butter!). You'll need to plan ahead for this dish as the cream should rest overnight.

French Lemon Cream Tart (from Dorie Greenspan's Baking from My Home to Yours)

Ingredients
1 9" tart shell, baked and cooled
1 cup sugar
Finely grated zest of 3 lemons
4 large eggs
1/2 cup fresh lemon juice (from 4-5 lemons)
1 cup plus 5 tablespoons (10-1/2 ounces) unsalted butter, cut into tablespoon-size pieces, at room temperature

1. Bring a few inches of water to a simmer in a saucepan.
2. Put the sugar and zest in a large heatproof bowl that can be set over the pan of simmering water.
3. Off the heat, rub the sugar and zest together between your fingers until the sugar is moist, grainy and very aromatic.
4. Whisk in the eggs, followed by the lemon juice.
5. 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. It takes a long time and your arm my feel like it's going to fall off, but don't stop whisking.
6. As soon as it reaches 180 degrees F, remove the cream from the heat and strain it into the container of the blender; discard the zest.
7. Let the cream stand, stirring occasionally, until it cools to 140 degrees F, about 10 minutes.
8. Turn the blender to high 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.
9. 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.
10. 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.