Pour the milk into a large mixing bowl. Add pudding mix.
Beat with electric mixer until well blended, 1 to 2 minutes. Let the mixture stand 5 minutes. Fold in whipped topping, using a rubber spatula. Spread the filling about 1/2" thick on one graham cracker. Press another graham cracker on top lightly and smooth the filling at edges with spatula.
Freeze until firm, about 4 hours. Wrap in plastic wrap and store in the freezer for up to 2 weeks.