Grate the truffle and combine it with 100g soft butter and the Pecorino. Sift your stock and bring it up to a low simmer. Finely dice the Onion.
Optionally slice the mushrooms into thick slices, then sautee in 20g of butter untill nicely caramelized, about 10-15 minutes.
Sauté the Onion in 20g butter until translucent (or just add to the mushrooms and) . Add tomato paste and and cook for 1 minute. Add rice and stir well. Cook for 2-4 minutes on medium heat untill it smells lightly toasted. Add whine and reduce by half, stirring often.
Add one Ladle of stock and cook, stiring often, untill mostly reduced. Repeat untill the desired doneness is reached, about 15-25 minutes. Turn off the heat, stir in the truffle butter, cover and let sit for 5 minutes. Season to taste with salt and black pepper