2.Stir through 3/4 of radicchio. Add rice and cook, 1 minute, stirring to coat with oil.
3.Stir in hot stock, 1 cup at a time. Allow liquid to fully absorb before adding more. Continue stirring gently, 15-20 minutes, until rice is just cooked.
4.Remove from heat and stir through parmesan, thyme and butter. Season to taste. Serve topped with remaining radicchio and grilled prosciutto slices, if you like.