Butternut squash risotto

Name: Butternut squash risotto
Ingredients: 30g/1oz unsalted butter; 2 tbsp olive oil; 1 onion, thinly sliced; 2 garlic cloves, finely chopped; 280g/10oz arborio rice; 200ml/7fl oz dry white wine; 1.1 litres/1 pint 16fl oz warm vegetable stock (made with stock cubes); 1 small (or ½ large) butternut squash, peeled, deseeded, cut into small cubes; small handful fresh sage leaves, thinly sliced; 100g/3½oz Parmesan (or a similar vegetarian hard cheese), finely grated; 150g/5oz ball of mozzarella, drained, cut into small cubes; 30g/1¼oz pine nuts, to serve; salt and freshly ground black pepper