In a large skillet, heat half of the olive oil on high heat. Add the sausage and cook until caramelized, breaking it up with a wooden spoon. Remove the sausage from the pot.
Add the remaining oil to the skillet and heat over medium-low with the garlic. Toast until golden. Add the chile flakes and toast for 1 minute. Add the onions and lower the heat. Cook until fragrant and soft.
Add the carrots and celery and cook until soft, another 5-10 minutes. Add the tomato purée and simmer for 1 hour on low heat. Season with salt to taste. Turn off the heat and fold in the herbs.
Towards the end of the cooking time, =bring a large pot of salted water to a boil. Add the pasta and cook according to package instructions. Drain the pasta, return to the pot, and drizzle with olive oil to prevent sticking.
Toss the pasta with the sauce, divide between bowls and garnish with herbs and ricotta salata.