(Pie Dough recipe from Cook's Illustrated, Chocolate Pastry Cream recipe from King Arthur Flour)
Step 1: Chocolate Pastry Cream
3 cups whole milk
1/2 cup sugar
1/4 tsp. salt
1/4 cup cornstarch
1 Tbps. all-purpose flour
4 large egg yolks
2 tsp. vanilla extract
1/4 cup (1/2 stick) butter
1 cup (6 ounces) good quality milk chocolate, finely chopped
For the Pastry Cream:
In a medium-sized saucepan, stir together 2 1/2 cups of the milk, the sugar, and salt. Bring to a simmer over medium heat, stirring to disolve the sugar.
Meanwhile, whisk the cornstarch, flour, and egg yolks with the remaining 1/2 cup milk.
Whisk some of the hot milk mixture with the egg yolks to temper them. This keeps the yolks from turning to scrambled eggs when you add them to the simmering milk.
Pour the egg/milk mixture back into the simmering milk. Doing this through a strainer will help prevent lumps later. Bring to a boil, stirring constantly with a whisk, until the mixture thickens.
Remove from the heat and strain through a fine sieve into a bowl that contains the butter, chocolate, and vanilla extract. Mix until everything is incorporated, cover with a piece of plastic wrap directly on the surface of the pastry cream to prevent a skin forming. Refrigerate until cool, and up to 5 days.