Home-Style Ham and Potato Casserole

8 potatoes, peeled and thinly sliced
2 onions, thinly sliced
1 tablespoon olive oil
1 pound country ham, thinly sliced
2 cups ricotta cheese
3 tablespoons chopped fresh rosemary
1 teaspoon black pepper
3 cups milk
1 cup grated Swiss cheese

Preheat oven to 375 degrees F.

Toss together the potatoes and onions and set aside.

In a large skillet over medium heat, heat the oil and add the ham. Saut