Preheat the oven to 375°F (190°C).
Bring a large pot of salted water to a boil and cook the ravioli according to the package directions, but boil for one minute less than the package recommends. Drain and set aside.
Place four oven-safe ramekins (about 5 inches diameter and 3 inches deep) on a baking sheet. Spoon one or two tablespoons of sauce into the bottom of each ramekin and spread slightly.
Put a single layer of 2–3 cooked ravioli in each ramekin (depending on ravioli size). Spoon about 1/3 cup sauce over the ravioli and spread evenly, then sprinkle about 1/3 cup shredded mozzarella on top.
Repeat the layers once more: another layer of ravioli, 1/3 cup sauce, and 1/3 cup mozzarella. Top with the remaining ravioli, divide the remaining sauce among the dishes, then finish with the remaining mozzarella and sprinkle with 1/2 cup grated Parmesan.
Bake for 20–25 minutes, until the cheese is melted and bubbling and the tops are lightly golden.
Let the ramekins cool for about 5 minutes before serving, as they will be very hot.