Instructions

• Make the pudding: In a large saucepan, whisk together 1¼ cups (250 g) granulated sugar, 6 tablespoons cornstarch, and 1 teaspoon salt. Whisk in 5 cups (1220 ml) whole milk until smooth.
• Cook the pudding: Place the saucepan over medium-high heat and heat, stirring constantly and scraping the bottom with a rubber spatula, until the mixture comes to a boil. As soon as it boils, reduce the heat to medium-low and continue cooking, scraping the bottom, until the pudding thickens and large bubbles appear on the surface, about 4 to 6 minutes.
• Finish the pudding: Remove the pan from the heat and whisk in 4 tablespoons unsalted butter (cut into pieces) and 5 teaspoons vanilla extract until smooth. Transfer the pudding to a large bowl, press plastic wrap directly onto the surface to prevent a skin, and refrigerate until cool, about 2 hours.
• Bloom the gelatin: While the pudding chills, stir 2 tablespoons water and 1.25 teaspoons unflavored gelatin together in a small bowl. Let it sit until the gelatin softens, about 5 minutes.
• Dissolve the gelatin: Microwave the bloomed gelatin until it is bubbling around the edges and visibly dissolved, about 15 to 30 seconds. Set aside to cool slightly (it should still be liquid).
• Make the stabilized whipped cream: Pour 2 cups (476 ml) heavy cream into a large mixing bowl. Using an electric mixer, whip on medium-low until foamy (about 1 minute), then increase speed to high and whip until soft peaks form (about 2 minutes). With the mixer on low, add the dissolved gelatin mixture, then increase to high and whip until stiff peaks form (about 1 minute). Be careful not to overwhip.
• Combine pudding and whipped cream: Whisk about one-third of the stabilized whipped cream into the chilled pudding to loosen it. Then gently fold in the remaining whipped cream in roughly 1/4-cup increments until the mixture is uniform and smooth.
• Prepare the pan: Line the bottom of a 9x13-inch baking dish with a single layer of the graham crackers (14 ounces), breaking crackers as needed to fit and cover the bottom completely.
• Layer the cake: Spread half of the pudding–whipped cream mixture evenly over the first graham cracker layer. Top with a second full layer of graham crackers. Spread the remaining pudding mixture over that layer, then finish with a final layer of graham crackers on top, pressing gently to level.
• Make the chocolate glaze: In a medium microwave-safe bowl, combine 1 cup (180 g) semisweet chocolate chips, 3/4 cup (178.5 ml) heavy cream, and 5 tablespoons light corn syrup. Microwave in 30-second intervals, stirring after each interval, until the mixture is smooth and fully melted, about 1 to 2 minutes total.
• Cool and pour the glaze: Let the glaze cool to room temperature, about 10 minutes, stirring occasionally. Pour or spread the cooled glaze evenly over the top layer of graham crackers.
• Chill and serve: Refrigerate the assembled cake for at least 6 hours (or overnight) before serving to allow the graham crackers to soften. Store leftovers covered in the refrigerator for up to 2 days.