Heat the butter and the oil together in a large saucepan until the butter melts.  Stir in the onion and garlic and cook for two to three minutes, without browning, until the onion has softened.   Stir in the butternut squash and cook for a further three to four minutes, until starting to brown.   Add 4 TBs of the stock, cover the pan and then allow to sweat over low heat for five minutes.   Add the rice and cook for a further couple of minutes, then pour in the wine.  Cook for two to three minutes until absorbed.   Stir in the stock 125ml (1/2 cup) at a time, stirring constantly, until most of the liquid had been absorbed.   Roughly chop one of the cheese rounds and then slice the other into four even slices.   Stir the chopped cheese into the risotto and season well with salt and pepper.   Add more liquid if need be.   The risotto is ready when the vegetables and rice grains are tender.  Remove from the heat and stir in the spinach. Cover and allow it to wilt with the heat from the risotto.   Serve immediately in bowls, topped each with a round of cheese, freshly ground black pepper and a drizzle of olive oil.