Usually ricotta/mozz. But since my mother used cottage cheese and mozz, sometimes I do it that way too… especially if we already have cottage cheese in the fridge. Not a purist (unless company coming) - have used shredded cheddar when using up a big bag of it. Will skip meat or use a chopped up leftover pork chop. And sliced zuc instead of noodles when there was a garden glut of it.