Summer Squash Gratin with greens

4 tablespoons butter 6 cups diced summer squash, 1/2-inch dice (yellow or green or combo) 1/2 cup chopped celery 1/4 cup chopped onion 1/2 cup sour cream 1[...]

2 cups small-curd nonfat cottage cheese or 2 cups low-fat cottage cheese 1 1/2 lbs summer squash (can be yellow, green or a mixture) salt , to taste 1/2[...]