Roast chicken risotto with chicken crackling

Name: Roast chicken risotto with chicken crackling
Ingredients: 1 leftover roast chicken carcass (you’ll need about 300-400g meat, and as much skin as you can get from the carcass); 1 carrot, halved lengthways; 2 onions, 1 unpeeled and halved, 1 peeled and finely chopped; 2 bay leaves; 2 chicken stock cubes; 25g butter, plus a large knob; 2 tbsp olive oil; 3 large garlic cloves, crushed; 300g risotto rice; 125ml white wine; ½ lemon, zested; small bunch of thyme, leaves picked; 50g grated parmesan, plus extra shavings to serve; truffle oil or extra virgin olive oil, for drizzling