Step 1: To make the crust, combine the finely crushed chocolate sandwich cookies and melted butter in a medium bowl. Press the mixture firmly and evenly into the bottom of a 9x13 inch baking dish. Place the dish in the freezer to chill while you prepare the next layers.
Step 2: For the cream cheese layer, beat the softened cream cheese and granulated sugar together in a large mixing bowl until smooth and creamy, about 2-3 minutes. Add 1 cup of cold milk and vanilla extract, beating until just combined. Gently fold in 1 1/2 cups of thawed whipped topping until no streaks remain. Spread this mixture evenly over the chilled cookie crust. Return the dish to the freezer for 15 minutes to firm up.
Step 3: For the chocolate pudding layer, whisk together the instant chocolate pudding mix, 3 cups of cold milk, and 2 tablespoons of hot chocolate mix in a separate bowl for about 2 minutes, or until the mixture is thick. Let it sit for 5 minutes to set further. Carefully spread this chocolate pudding layer over the cream cheese layer. Place the dish back into the refrigerator for at least 30 minutes to an hour to allow the pudding to set completely.
Step 4: Once the pudding layer is firm, gently spread the remaining 3 cups of thawed whipped topping evenly over the chocolate pudding layer.
Step 5: Decorate your Hot Chocolate Lasagna by sprinkling generously with mini chocolate chips, chocolate shavings, a dusting of hot chocolate mix, or mini marshmallows. Cover the dish loosely with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, to allow all the layers to set and the flavors to meld beautifully.
Step 6: When ready to serve, remove from the refrigerator, slice into squares, and enjoy your delicious Hot Chocolate Lasagna!