In a medium saucepan, heat the milk with 1/4 c. of the sugar until bubbles form around the edge. In a large bowl, whisk the egg yolks with 1/4 c. of the sugar, the cornstarch and salt. Gradually whisk in the hot milk mixture. Pour the mixture into the saucepan and cook over moderate heat, whisking constantly, until very thick, about 3 minutes. Remove from the heat and whisk in the semisweet and unsweetened chocolate until smooth.
You can put this pudding into individual cups or one medium bowl.
You can also put this filling into a baked pie crust, a graham cracker crust or a chocolate crumb crust.
If making a pie, the pie needs to be refrigerated for at least 3 hours before you cut it.
All of these servings benefit from putting homemade whipped cream on top!