1 (15-ounce) container whole milk ricotta cheese
1 (10-ounce) package frozen chopped spinach, thawed, squeezed dry
4 ounces thinly sliced prosciutto, chopped
2 large egg yolks
3/4 teaspoon salt
1/2 teaspoon freshly ground black pepper
48 wonton wrappers
1/2 cup (1 stick) butter
1 1/2 teaspoons dried oregano
Freshly grated pecorino