How to Make It
Preheat the oven to 350°. Spread the shelled pistachios on a rimmed baking sheet and bake for 5 minutes, or until lightly toasted. Let cool completely, then rub the pistachios in a kitchen towel to remove the skins. Transfer the pistachios to a food processor and grind to a fine powder.
In a medium saucepan, combine the milk with the pistachios and bring to a boil. Cover, remove from the heat and let stand for 30 minutes.
Strain the pistachio milk through a fine sieve into another medium saucepan. Add the sugar and a pinch of salt. Whisk in the egg yolks and cook over low heat, whisking constantly, until the custard sauce is thick enough to coat the back of a spoon, about 8 minutes. Do not let the custard boil.
Strain the sauce through a fine sieve into a bowl. Stir in the almond extract and let cool, stirring often. Cover and refrigerate until ready to serve.