How to Make It
In a medium saucepan, combine 1 3/4 cups of the heavy cream with the milk and granulated sugar and bring to a bare simmer over moderately low heat, stirring occasionally, about 12 minutes. Meanwhile, sift the cornstarch and cocoa powder into a medium bowl, then whisk in the eggs and the remaining 1/4 cup of heavy cream to form a smooth paste. Gradually whisk 1 cup of the hot milk into the cornstarch mixture, then scrape the mixture into the saucepan and cook over moderately low heat, stirring constantly, until the pudding is thick enough to coat the back of a spoon, about 30 minutes.
Put the chopped chocolate in a heatproof medium bowl and set a fine sieve over it. Strain the pudding over the chocolate and let stand for 3 minutes. Whisk until smooth, then whisk in the butter and salt. Press a sheet of plastic wrap directly on the surface of the pudding and refrigerate until chilled, about 3 hours.
In a medium bowl, using a hand mixer, beat the heavy cream with the confectioners’ sugar, vanilla and salt until firm, about 5 minutes.
In a 3-quart trifle bowl, make 4 layers each of the pudding, whipped cream and crushed cookies. Serve.