To cook the salmon fillets, heat a non-stick frying pan until hot and add 1-2 tablespoons olive oil. Fry the salmon, skin side down, for 3 minutes. Flip over and cook the other side for 1-2 minutes. The flesh should be slightly springy when pressed. Season lightly.
Add the mint leaves to a medium pan of boiling salted water. Bring back to the boil, then add the peas and blanch for 2–3 minutes until they are just tender and bright green. Drain, reserving the liquor.
Tip the peas and mint into a blender. Add just enough of the reserved liquor to cover the peas and whiz to a smooth, bright green purée. Add the butter and all but 4 tbsp crème fraîche. Season and pulse for a few seconds to combine.
To serve. Place the salmon off centre and spoon the pea puree next to the salmon. Accompany with a dollop of crème fraîche.
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