Crab saffron risotto

Name: Crab & saffron risotto
Ingredients: 1 tbsp oil; 1 onion or banana shallot, finely chopped; 1 garlic clove, crushed; 380g risotto rice (arborio or carnaroli); 200ml white wine; 1-1.3 litres hot fish or chicken stock; 30g cold butter; 100g white crabmeat; 100g brown crabmeat; large pinch of saffron strands; 70g parmesan, grated; 1 lemon, zested, half juiced; 1 tbsp finely chopped tarragon or dill