In a large bowl, combine ham and onions; place about ¼ cup down the center of each tortilla. Top with 2 tablespoons cheese. Roll up and place seam side down in a greased 13x9-in. baking dish.
In another large bowl, combine the flour, cream, eggs and, if desired, salt until smooth. Pour over tortillas. Cover and refrigerate for 8 hours or overnight.
Remove from the refrigerator 30 minutes before baking. Cover and bake at 350° for 25 minutes. Uncover; bake for 10 minutes. Sprinkle with remaining cheese; bake 3 minutes longer or until the cheese is melted. Let stand for 10 minutes before serving.
