In order to make this filling you will need a double boiler. If you don't have a double boiler, use a heat safe bowl set over a sauce pan. Fill the sauce pan with about an inch of water and set the bowl over the water, making sure the bowl doesn't actually touch the water. You'll also need either a blender or food processor.
Lemon Cream Tart Filling
Recipe from Dorie Greenspan's Baking: From My Home To Yours
1 cup sugar
Zest of 3 lemons
4 eggs
3/4 cup lemon juice (from 4-5 lemons)
1 cup plus 5 T unsalted butter, at room temperature, cut into small pieces
Prepared pie or tart crust
Blueberry Coulis (see below)
Set pan of water over medium heat. In heat safe bowl, combine sugar and lemon zest. Rub the sugar and zest together with your fingers until the sugar is moist and grainy. Whisk in the eggs, one at a time, followed by the lemon juice.
Set the bowl over the pan and whisk as soon as the mixture begins to heat. Stir constantly to keep the eggs from scrambling as the mixture cooks. Heat the mixture to 180 degrees. The mixture will start off thin and foamy, but will quickly turn thicker. Once the whisk leaves a trail through the mixture, it is almost done. This process will generally take about 10 minutes. The cream will be thick and shiny when it's ready.
When the mixture has reached 180 degrees, pour through a fine mesh strainer into blender or food processor. Let it cool for about 10 minutes, until the temperature falls to about 140 degrees. Turn the blender on high and through the center of the lid, add pieces of butter a couple at a time. Occasionally scrape down the sides of the bowl as it processes, until all the butter is incorporated. Once the butter is all mixed in, continue to blend an additional 3 minutes.
Transfer the lemon cream to a clean bowl and cover with a sheet of plastic wrap, pressing the plastic directly against the cream to prevent a skin from forming. Cover with lid and refrigerate for at least 4 hours.
Preheat oven as directed on crust package or recipe. Roll out pie or tart crust on a well-floured surface. Transfer to tart pans and press lightly in place. Cover crust with a sheet of foil, pressed against the surface. Fill with dried beans or rice and bake about 7-10 minutes. Remove foil and beans and prick the surface of the dough with a fork several times and continue baking about 5-10 more minutes until golden brown. Remove from the oven and let cool.
Blueberry Coulis
1 cup fresh blueberries
1 T sugar
Empty blueberries into a food processor. Sprinkle with sugar and pulse several times until blended. Refrigerate until ready to serve.
When cream is ready, spoon into tart shells. Top with blueberry coulis and serve.