1 stick plus 1 tablespoon cold unsalted butter, cut into small pieces
1 large egg, lightly beaten
1 large egg yolk
2 cups milk
3 large egg yolks
1/4 cup sugar
2 tablespoons all-purpose flour
1/2 cup finely crushed amaretti (about 3 ounces)
Combine the flour and salt in a food processor. Add the butter and pulse until the mixture resembles coarse meal. In a small bowl, combine the beaten egg with the egg yolk. Add it to the flour mixture and pulse just until a smooth dough forms. Gather the dough into a ball and divide it into 2 pieces, 1 slightly bigger than the other; pat each piece into a disk. Wrap the disks of dough well in plastic or wax paper and refrigerate for at least 1 hour or overnight.
In a heavy medium saucepan, heat the milk just until steaming. In a large heatproof bowl, whisk the egg yolks with the sugar until pale. Whisk in the flour. Whisk in 1/2 cup of the hot milk, then whisk the egg mixture into the milk in the saucepan until blended. Cook over moderate heat, stirring constantly with a wooden spoon, until the custard comes to a boil and has the consistency of thick pancake batter, about 7 minutes. Transfer the custard to a bowl and press a piece of plastic wrap directly on the surface. Let the custard cool completely.
Preheat the oven to 375°. On a lightly floured surface, roll the larger disk of dough out to a 13-inch round. Ease the dough into a 10-inch tart or cake pan with a removable bottom, pressing it into the corners. Fold the overhanging dough into the pan and press it against the side. Spread the cooled custard in the pan and sprinkle the amaretti crumbs evenly over the top.
Roll the remaining dough out to an 11-inch round and set it over the custard. Pinch the edges together to seal the dough. Trim any overhang with a sharp knife. Prick the top crust with a fork and bake for 35 to 40 minutes, or until the pastry is golden and the custard is steaming through the top crust. Let the crostata cool completely before unmolding and serving.
The crostata can be stored at room temperature for up to 8 hours before serving.