1. Prepare the Filling: In a large bowl, whisk together the instant vanilla pudding mix and 3 cups of milk until thickened (about 2 mins). In a separate bowl, whip the heavy cream to stiff peaks. Gently fold the whipped cream and 2 teaspoons of vanilla into the pudding mixture.

2. Layer the Crackers: Line the bottom of a 9×13-inch baking dish with a single layer of graham crackers. Break pieces to fit the corners if necessary.

3. Assemble Layers: Spread half of the pudding mixture over the crackers. Add a second layer of crackers, followed by the remaining pudding. Finish with a third and final layer of graham crackers.

4. Make Chocolate Topping: In a small saucepan over medium heat, melt the butter. Whisk in cocoa powder, powdered sugar, 1 teaspoon vanilla, and 3 tablespoons milk. Stir until smooth and glossy, then remove from heat.

5. Glaze: While the glaze is still warm, pour it over the top layer of graham crackers and spread evenly to the edges.

6. Chill: Cover and refrigerate for at least 4 to 8 hours (preferably overnight). This ‘icebox’ step is crucial for the crackers to soften into a cake-like texture.