Prepare the chocolate cake as recommended above.
To prepare the chocolate pudding filling: In a large bowl, on the medium speed of an electric mixer, beat the instant pudding and the milk for 3 minutes. Place uncovered in the refrigerator and chill until set, about 15 minutes.
Meanwhile, in a medium-size bowl, whip the heavy cream with the sugar and the vanilla extract until soft peaks form, being careful not to overwhip.
To assemble the trifle: Place 1/3 of the cake in the bottom of a large glass bowl. Place over this 1/3 of the pudding mixture, spreading evenly with a rubber spatula. Spread 1/3 of the whipped cream over this. Sprinkle with 1/3 of the cookie crumbs. Proceed in this fashion until three layers have been assembled, ending with a dusting of the cookie crumbs. Refrigerate at least 2 hours, or overnight, before cutting and serving.
The Magnolia Bakery Cookbook, Simon & Schuster