Cheesy truffle risotto your way

Name: Cheesy truffle risotto your way
Ingredients: 15g butter; 1 tbsp olive oil; 1 onion finely chopped (save the skin and trimmings for the stock); 150g risotto rice; 100ml white wine; 20g parmesan or vegetarian alternative, finely grated; 2 tbsp truffle paste; 1 tbsp mascarpone; 750ml vegetable or chicken stock; parmesan rinds or vegetarian alternative (add as many as you have); small handful of flat-leaf parsley stalks only (saving the leaves to serve); ½ tsp black peppercorns; 2 chestnut mushrooms; 1 hazelnut; truffle or extra virgin olive oil, for drizzling