6 thin bars (1.55 ounces each) milk chocolate, broken into single sections and each section broken in half, OR about 9 ounces (1-1/2 cups) milk chocolate chips
3 to 4 large, ripe bananas
About 12 to 14 double Graham crackers, each broken in half
2/3 cup granulated sugar
4 tbsp. cornstarch
Pinch of salt
4 or 5 egg yolks, from eggs graded "large" (when my yolks have been on the small side, I've used the greater number here)
4 cups (1 quart) whole milk
4 tbsp. (1/4 cup or 1/2 stick) unsalted butter, cut into thin slices, preferably at room temperature
1 tbsp. vanilla
Have ready the milk chocolate pieces or chips and the ripe bananas. Line the bottom of your pan with a layer of graham crackers, fitting them together as tightly as possible. If there are any holes or gaps, break off pieces of graham cracker to fit them. Set everything aside near your stovetop.
Off heat, in a 3 quart, heavy-bottomed pot, combine sugar, cornstarch, and salt. Mix well with whisk or slotted spoon, getting out as many lumps as possible. Set aside. In small bowl, combine yolks with about 2 Tbsp. milk (no need to measure); with fork, beat until well-mixed. Add mixture to 3 quart pot. Stir with whisk or slotted spoon just until mixed; do not beat!
In 1-1/2 to 2 quart heavy-bottomed pot, heat remaining milk over low heat, stirring often, until very hot. Remove milk from heat. Stirring yolk-cornstarch mixture constantly, very gradually add hot milk. When all milk has been added, scrape down sides and bottom of pot with heat-resistant rubber spatula. Place 3 quart pot over medium heat; keep stirring gently but constantly. There will be a layer of foam on top of this milk mixture-OK.
Continue stirring mixture over medium heat until it begins to boil (you can stop stirring momentarily to check for this; bubbles should break on the surface of the mixture). Boil, stirring constantly, for 90 seconds; the foam layer should incorporate into the thickening pudding. Remove from heat; add butter and vanilla. Let stand for a few seconds, then gently stir to incorporate butter and vanilla. From here on out, work quickly.
Strain the pudding through the fine strainer into the heatproof measuring cup. Pour about one-third of the hot pudding over a spatula onto the graham cracker layer in the bottom of your pan (pouring over a spatula allows you to pour without disturbing this layer so much); if necessary, spread the pudding quickly with a spoon to form an even layer. Peel a banana and remove any bruised spots; slice the banana into slices about one-quarter inch thick and place a layer of the slices, cut side up, into the pudding (I like to place slices right next to one another-you'll use more banana that way, though. You can use a lesser amount of banana if you wish). You may need to use more than one banana for your first layer of slices, but don't use more than half of the bananas you have. After the layer of banana slices, sprinkle on half of the chocolate pieces or chips.
If a "skin" has begun to form on top of your pudding, stir it back in. Pour about half of the remaining hot pudding over a spatula onto the chocolate layer, again spreading it evenly if necessary. Don't worry if you swirl some of the melted chocolate into the pudding as you're spreading the latter. Slice the remaining banana(s) and place a layer of them, cut side up, into the pudding, followed by a layer of the remaining chocolate pieces or chips. Pour the final third of your pudding over a spatula onto the top chocolate layer, spread it evenly, then top the pudding with a layer of graham crackers, right side up. Again, if there are any gaps in this top graham cracker layer, break pieces off from other graham crackers as necessary to fill them in. Very gently, with the palm of your hand, press down slightly on the top layer of graham crackers to flatten and even out the dessert.
Place into the refrigerator and chill for at least three hours before serving. To serve, you'll need a broad-bladed spatula and/or large spoon; this is not a particularly neat dessert! Serve within about 12 hours of completion.