1. Preheat your oven to 375°F or 190°C.

2. Cook the pasta until it's al dente, following the package instructions, then drain and set it aside.

3. In a large pan, melt the butter over medium heat and add the diced onion, sautéing until it becomes translucent.

4. Add the meatball mixture to the pan, breaking it apart with a spoon as it cooks, and continue until it's browned on all sides.

5. Next, add the tomato puree, chili paste, and beef stock to the pan, stirring well to combine, and bring the mixture to a simmer.

6. Slice the spicy sausages and add them to the pan, stirring again to combine.

7. In a large baking dish, combine the cooked pasta, meatball mixture, and sliced sausages.

8. Cover the dish with aluminum foil and bake in the preheated oven for 20 minutes.

9. Remove the foil and bake for a further 10 minutes, or until the top is lightly browned.

10. Serve the dish hot, accompanied by a side salad.