To cook the mussels: Pour the wine into a large sauce pan, add the shallots, garlic and chilli and bring to a simmer. Then add the mussels, cover and cook over a high heat for about 3 minutes, shaking occasionally. Discard any mussels that haven’t opened after this time. Strain the remaining mussels in a sieve set over a bowl.
To cook the hake: Heat the oil and butter in a frying pan large enough to take the 4 fillets of hake. Add the hake, skin side down, and cook over a medium heat for 2-3 minutes, then turn the fillets and cook for a further 2-3 minutes.
To make the sauce: Meanwhile you can make the sauce in the pan you cooked the mussels in. Put it back on the heat and add the cooking liquid. Stir in the crème fraîche and parsley and season with salt and pepper. Add the mussels back into the sauce pan to heat up.
To serve: Serve the hake with the mussels and sauce spooned over. Delicious with a green salad and crusty bread.