2 tablespoons olive oil
1 1/2 cups diced yellow onions (1/4-inch dice)
4 cloves garlic (minced)
1 1/2 pounds rainbow or Swiss chard (stems removed, leaves cut crosswise into 1-inch ribbons)
  Freshly ground black pepper (to taste)
1 cup grated mozzarella cheese
1 cup grated provolone cheese
1 cup grated parmigiano Reggiano or Pecorino Romano cheese
1/2 cup ricotta cheese
2 tablespoons unbleached all-purpose flour
3/4 cup heavy (whipping) cream
4 large eggs
1 cup milk
8 ounces thinly sliced prosciutto ham