An unconventional combination: the flavors of a Boston cream pie are transformed into a casserole-style dessert that does not need any time in the oven. Homemade pudding is layered with a crunchy graham crackers and fudgy chocolate frosting. After it rests overnight in the refrigerator, it takes on a cake-like consistency, kind of like an icebox cake.
Adapted from Faith Durand's "Not Your Mother's Casseroles."
Line the bottom of a 9-by-13-inch baking pan with graham crackers, using about a quarter of them and breaking some in half, if necessary. Set aside.
For the custard:
Place the cornstarch in a small bowl. In a second small bowl, whisk together the eggs and egg yolks. Set both aside.
In a deep, heavy saucepan, melt the butter over medium heat and stir in the sugar. Add the salt and half-and-half, and stir. Warm over medium heat until bubbles form around the edges of the liquid. Do not let it boil. When the half-and-half mixture is hot, turn off the heat.
Pour a ladleful of the hot half-and-half mixture into the cornstarch. Whisk vigorously to combine. The mixture should come together smoothly, with no lumps; if there are any lumps, add a little more liquid and whisk them out. Pour this cornstarch mixture into the beaten eggs. Whisk vigorously to combine.
Pour the egg mixture into the saucepan with the remaining half-and-half mixture, and turn the heat to medium. Whisk continously and vigorously, working all angles of the pot and scraping the bottom. Continue whisking for about 5 minutes, or until the custard becomes very thick and starts to boil, with large bubbles that slowly rise to the surface. Turn off the heat and stir in the vanilla.
Spread one-third of the pudding evenly over the graham crackers. Top with a layer of one-third the remaining graham crackers, and spread a half of the remaining pudding over that layer. Add a third layer of graham crackers and top with the remaining pudding. Cover the top of the pudding with a final layer of graham crackers. Set aside.
For the frosting:
Melt the butter with the cocoa powder in a small saucepan. Bring to a light simmer over medium-low heat and let it bubble for 1 minute. Whisk in the milk and cook for 3 more minutes, letting the mixture bubble up around the edges. Remove from the heat and beat in the confectioners' sugar with a whisk or hand beater. When the mixture is smooth, beat in the vanilla. While the frosting is still quite hot and liquid, pour it over the top layer of graham crackers and smooth it with a hot knife or a spatula dipped in hot water.
Cover the layered dessert with a lid or aluminum foil and refrigerate (if using foil, be careful not to let it touch the top of the dessert, as it will stick to the frosting and spoil the look). Refrigerate for a minimum for 4 hours and up to 2 days before slicing and serving. Serve chilled.