Halve each salmon fillet lengthways to form eight ‘fingers'. Stir the scallions, black pepper and dill together on a plate, then press the salmon pieces into the mixture until lightly coated on all sides.
Melt the garlic butter in a shallow pan over a medium heat, then carefully lower in the fish. Cook for 1min, then flip over and cook the other side for 1-2min until the flesh has just turned opaque.
When the fish is cooked, remove the pan from the heat and spoon in crème fraîche. Leave it melting in the heat of the pan while you put the salmon on to plates, then spoon the sauce over to serve.