Put all but 11 g of the (1 ½) cups of grated cheese in a large, deep, heat resistant bowl.
Pour 187,5 ml of boiling chicken stock over the cheese and, using an immersion blender, blend on high speed until the cheese begins to melt.
Or transfer the mixture to the jar of an electric blender and blend on high speed.
With the blender running, add the 30 ml olive oil and truffle oil (if using) and continue blending until the sauce is smooth and emulsified.
When blended, pour the sauce into a small pan, cover and keep warm over very low heat.
In a large skillet, melt the butter over medium-high heat.
Add the onion and garlic and cook, stirring until the onion is translucent, 1 to 2 minutes.
Stir in the radicchio, prosciutto, the remaining (1 cup of) boiling chicken stock, and thyme.
Return to a boil then adjust the heat down to medium-low and simmer until heated through, 2 to 3 minutes.
Season to taste with salt and pepper.
Bring a large pot of salted water to a boil.
Stir in the pasta and cook until al dente, about 2 minutes for fresh pasta, then drain.
For dried pasta, follow the manufacturer’s directions.
While the pasta is boiling, remove the sauce from the heat.
Stir in the reserved grated cheese.
Add the pasta to the sauce and turn to coat evenly.
Divide the pasta among 4 large plates.
Sprinkle with additional cheese, ground black pepper, drizzle a little olive oil over the pasta and serve at once.