HALIBUT, MUSSEL AND SAFFRON STEW

small pinch saffron • 2 tbsp olive oil • 1 fennel bulb, trimmed and chopped • 2 leeks, trimmed and finely sliced • 1kg fresh mussels, cleaned • 400g cherry tomatoes • 2 garlic cloves, roughly chopped • 300ml Paul Mas Viognier/Sauvignon • 400g halibut fillet (fresh, or frozen and defrosted), skinned and cut into 2cm cubes • 25g flat leaf parsley, finely chopped • toasted sourdough, to serve