Halve each salmon fillet lengthwise to form eight fingers. Stir the spring onions 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 medium heat and carefully lower in the fish. Cook for one minute, then flip over and cook the other side for one to two minutes until the flesh has turned opaque. When the fish is cooked, remove it from the pan. Switch off the stove, spoon creme fraiche into the pan and let it melt in the residual heat, while you put the salmon onto the plates. Spoon the sauce over the fish to serve.