9 oz. graham crackers
3 tbsp. unsalted butter
2 - 14 oz. cans of sweetened condensed milk
9 oz. chocolate
For crust: Melt the butter in a small saucepan over medium heat. While the butter is melting, grind the graham crackers in a food processor until it is all crumbs. Pour the butter into the food processor bowl and pulse a few times to mix thoroughly. Pour the crumb mixture into a removable bottom tart tin (round or rectangular). Use the back of a spoon to press the crumbs firmly into place along the bottom and side of the tin. Refrigerate to set.
For filling: Fill a pasta pot 2/3 full of water. Take the cans of condensed milk and remove the labels. Place in the water, make sure the cans are covered by at least 2-3 inches of water. Turn on the heat to high, and cover. Once the water comes to a boil, turn the heat down to maintain a simmer, keep covered. Leave for 3 hours.
Once cooked, carefully move a can into a metal bowl. Place an opener on the edge of the can using one hand and hold a tea towel over the top of the can with the other hand. The condensed milk is under pressure after having been cooked for several hours. When you first open the can it can spill out. Making a single puncture while covering the top releases the pressure while safely containing extremely hot and sticky caramel. After the pressure has been released remove the towel and open normally. Repeat with the other can. Pour the caramel into a bowl and cool. (Can be made a day ahead.)
To assemble: Melt the chocolate in a double boiler. Pour a thin layer into the bottom of the crust and let set for a few minutes in the fridge. Once set, pour in the caramel and smooth the top. Drizzle the remaining chocolate over the top of the tart anyway you like. Let set.