Boil the rice in plenty of salted water and drain when al dente.
In a bowl, beat the eggs with the cheese, salt and freshly ground pepper; add the diced mozzarella and prosciutto.
Butter an oven dish, pour the rice into it, and cover it with the terrine ingredients.
Place the dish back on low heat and stir until the mozzarella cheese has melted.
Notes
For an even more flavorful version, you can add a tablespoon of concentrated tomato sauce to the terrine. This will give the risotto a more intense flavor and a pleasant hint of color. Remember to adjust the salt and pepper to your taste.