1. Preheat the oven to 425°F (220°C).

2. Cook the rice according to the package instructions and set it aside.

3. Cut the sausage into thin strips and peel and chop the onions. In a large skillet, cook the sausage over medium heat until it's lightly browned. Then add the onions and cook until they're softened. Stir in the tomato puree and cook for 1 minute.

4. Gradually add the heavy whipping cream and milk to the skillet, whisking continuously. Bring the mixture to a boil, then reduce the heat and simmer for 5 minutes. Season with Dijon mustard, salt, and pepper.

5. Grease a 9x13-inch (23x33 cm) baking dish and spread the cooked rice evenly across the bottom. Top the rice with the sausage and sauce mixture, followed by the halved cherry tomatoes and shredded cheese blend. Bake in the preheated oven for 15 minutes, or until the top is golden brown and the sauce is bubbly.

6. Garnish with fresh basil leaves if desired.