Raspberry Gratin

0 In a medium heavy-bottomed pot, bring the milk to a boil, and then turn off the heat. Whisk the egg yolks together in a medium bowl, and then whisk in ½ cup sugar and cornstarch. Continue whisking until the mixture thickens and is a pale-yellow color. 
5 Slowly whisk in the hot milk, at first a few tablespoons at the time, and then more quickly. Return the mixture to the stove, and cook over medium heat, alternating between the whisk and a spatula, until the pastry cream thickness to a pudding-like consistency.
1 Remove from the stove and stir in the butter and salt. Transfer the mixture to a bowl. Place a piece of plastic wrap on the surface to keep it from forming a skin. Poke a few holes in the plastic to let the heat escape. Cool in the refrigerator.
2 When the custard has cooled, fold in the crème fraiche.
3 Preheat the broiler. Toss the raspberries with 1 tablespoon granulated sugar, and scatter half of them on the bottom of a 9 by 9-inch gratin dish. Spoon the custard over the raspberries. Scatter the remaining raspberries on top. Sift the confectioners’ sugar over the top and pass under the broiler for about 7 minutes, until bubbling and gratineed on top.
4 Serve the gratin at the table with a big serving spoon.