Flake tuna with fork in large bowl. Add soup with wire whisk, substitute milk for water, instead of 2 cans of water-use 1 1/2 cans of milk. Mix well. Add sour cream and continue to whisk, no lumps.
Butter a large casserole baking dish. Now crunch with hands a good layer of chips into bottom of dish. Pour over 1/3 of tuna mixture, and spread with back of spoon. Now add a layer of cheese, spread evenly-and continue with 2 more layers of chips and tuna mixture.
If your casserole has no lid, cover with foil, tented, so cheese doesn't stick, and place in oven at 325 degrees for about 25 minutes.
Remove lid/foil and let bubble about 8 to 10 minutes. Remove from oven, and allow to cool about 15 minutes. Cut lasagna style and serve.