Soak dried porcini mushrooms in boiling water for at least 20 minutes.
Heat 3 tablespoons oil in a pan over medium heat; add shallot and cook for 1 minute to soften. Add sliced radicchio and 120ml white wine; simmer until radicchio has wilted. Season with salt and black pepper and set aside.
Melt 2 tablespoons butter and 1 tablespoon oil in a heavy-based saucepan over medium heat; add shallot and cook for 1 minute to soften. Stir in rice to coat in oil; add wine and simmer until liquid has nearly evaporated. Add hot stock, one ladle at a time, stirring constantly and adding more stock when the liquid is absorbed.
Stir in rehydrated mushrooms and 1 ladle of mushroom liquid; simmer for 1 or 2 minutes. Add shallot-radicchio mixture and stir to heat through.
Remove risotto from heat; stir in butter and let risotto rest for a few minutes. Spoon into bowls and top with freshly grated Parmesan cheese.