This dish is like breadcrumb-crust cake filled with Arborio rice, sausage, ground turkey or beef, tomatoes and cheeses.
In a large saucepan combine the rice, chicken broth, 1 1/4 teaspoons of the salt and the bay leaf. Stir and bring to a boil over high heat. Cover the pan with a tight-fitting lid, reduce the heat to low and simmer, stirring once, until the rice is still slightly undercooked but the liquid is absorbed, 8 minutes. Pour the rice into a large bowl and cool to room temperature, stirring occasionally. Stir in 2 1/2 cups of the cheese and 3 of the eggs until well combined, and set aside.
Meanwhile, heat the extra-virgin olive oil in a medium nonreactive saucepan over medium-high heat. Remove the sausage from the casing and break into small, bite-size pieces. Add the sausage to the hot oil and cook until browned, breaking it up with the back of a wooden spoon as it cooks. Using a slotted spoon, remove the sausage to a medium bowl and set aside. Reduce the heat to medium and add the garlic, shallots and 1/4 teaspoon of the salt. Cook, stirring constantly until fragrant and the shallots are soft, 1 minute. Add the basil, cheese rind and tomatoes, and bring to a simmer. Reduce the heat to low and simmer, stirring occasionally with a wooden spoon for 15 to 20 minutes.
Remove the basil and cheese rind. Add 2 cups of the sauce to the reserved sausage and set aside.
Meanwhile, in a separate medium bowl, mix together 2 tablespoons of the breadcrumbs, the milk and the remaining egg with a fork and let the mixture sit for 5 minutes to thicken. Stir in the oregano, the remaining 1/4 teaspoon salt and the remaining 1/2 cup cheese. Using your hands, mix in the beef, until just combined. Heat 1/2-inch of olive oil in a medium straight-sided pan. Scoop 1-tablespoon mounds of the mixture into damp hands and roll into uniform balls. When the oil is hot, fry the balls in 2 batches, turning them as needed with a slotted spoon to brown the balls evenly, about 4 minutes. When golden brown and crispy all around, remove the balls using a slotted spoon to the bowl with the sausage and sauce. Continue with the remaining balls, and then toss to coat evenly in the sauce.
Preheat the oven to 350ºF. Using 1 tablespoon of the butter, grease the inside of a Bundt pan or a 3 1/2-quart Dutch oven, making sure to coat it very well. Dust the inside of the pan with 3 tablespoons of the breadcrumbs. Make sure it is evenly coated and there are no bald spots. This is very important to prevent sticking.
Add the peas and diced mozzarella to the meat and sauce, and toss gently to incorporate. Spoon two-thirds of the rice mixture into the prepared bundt pan. Using damp hands, press the rice evenly over the bottom of the pan and 2 1/2-inches up the sides and middle of the pan. Spoon the meat filling into the well of rice and press gently to make sure it is evenly packed. Spoon the remaining rice over the filling and, using damp hands, press the rice evenly over the filling, being sure to press the rice on top into the rice along the edges to seal. Sprinkle evenly with the remaining 2 tablespoons breadcrumbs and dot with the remaining 1/2 tablespoon butter. Bake until lightly browned on top, 45 minutes.
Cool for 15 minutes.
Place a plate large enough to cover the top of the pan over the pan. Using heat-resistant pads or a towel, invert the sartu onto the plate. Carefully lift the pan off of the rice, shaking gently if needed. Warm the remaining sauce and fill the opening in the middle of the molded rice with the sauce to serve.