The lemon cream will keep wrapped tightly in the fridge for 3 days. Assembly of the tart should be done on the same day as you plan on eating it.
For the tart base, use the same tart base for the Blueberry Tart(s) http://rhid-baked.blogspot.com/2007/07/blueberry-tarts.html
Ingredients: Filling
1 cup sugar
Grated zest of 3 lemons
4 large eggs
3/4 cup freshly squeezed lemon juice (from 4-5 lemons)
2 sticks + 5 Tbs. of butter, at room temp, cut into 1 Tbs pieces.
2 sticks + 5 Tbs. of butter, at room temp, cut into 1 Tbs pieces.
Method
Have an instant read thermometer, a strainer and a blender at hand.
1.Bring a few inches of water to boil in a saucepan.
2. Put the sugar and zest in a large heatproof bowl (that will fit inside your saucepan of simmering water). Off the heat, rub the sugar and zest together between your fingers until the sugar is moist, and very aromatic.
3. Whisk in the eggs, and then add the lemon juice.
4. Set the bowl over the pan and start stirring with the whisk as soon as the mixture feels tepid.
5. Cook the lemon cream until it reaches 180F(around 82C) whisk the lemon cream the whole time.
6. Once it has reached 180F, remove it from the saucepan of simmering water and strain it into the blender. Throw away the lemon zest.
7. Wait until the temperature of the lemon cream is 140F before turning the blender on.
8. Once it is 140F, turn on the blender, and proceed to feed the butter into the lemon cream 5 Tbs at a time. Make sure you periodically scrape down the sides of the blender.
9. Blend for 3 min. on the highest setting - this makes the cream lighter and airier.
10. Refrigerate for at least 4hours.
11. Put into a cooled tart base, and add raspberries if desired.
Taken from Dorie Greenspans book "Baking: From My Home to Yours" pp. 331-33.