Heat a pan over medium-high heat. Add the olive oil. Once hot, add the onion and the sausages and using a wooden spoon, break up the sausages into small pieces as you brown them. Add the mint and bay leaves and continue to cook.
Once the sausage is golden brown, add the wine to the pan, and stir away, let the alcohol evaporate, then lower the flame and season with salt and pepper. Add the walnuts and let the sauce slowly simmer for about 5 to 10 minutes.
Cook the pasta in a large pot of salted boiling water according to package directions for al dente.
When ready to serve, add the radicchio to the sauce, and stir well. Cook's Note: You want to wait until the last minute to make sure that it stays crunchy, as opposed to wilted and cooked down.
Add the cooked pasta and toss. Add some grated Parmesan, to taste. Serve immediately.