In a medium bowl, whisk together the instant vanilla pudding mix and 3 cups of milk for about 2 minutes until thickened.

Gently fold in half of the thawed whipped topping until smooth and creamy.

In a 9x13-inch pan, lay a single layer of graham crackers to cover the bottom completely.

Spoon half of the pudding mixture over the graham crackers and spread evenly.

Add another layer of graham crackers on top of the pudding mixture and spread the remaining pudding mixture evenly over it.

Finish with one last layer of graham crackers on top.

In a small saucepan over low heat, melt unsweetened chocolate and ¼ cup of butter.

Stir until fully melted and mix in 2 tablespoons of milk and 2 cups of powdered sugar until glossy and pourable.

Pour the chocolate glaze over the top layer of graham crackers and spread it evenly.

Refrigerate for at least 4 hours or overnight to chill and set.

Once chilled, slice into squares and serve chilled.