How to Make It
In a large saucepan of boiling water, cook the peas until tender, 3 to 4 minutes; drain. In the same saucepan, melt 1 tablespoon of the butter in the cream. Add the peas and mash with a potato masher until chunky. Season with salt and pepper and keep warm.
In a small saucepan, simmer the wine with the lemon juice over moderate heat until reduced to 1 tablespoon, 8 to 10 minutes. Reduce the heat to low and whisk in the remaining 6 tablespoons of butter, one cube at a time, until the sauce is thickened. Whisk in the tarragon and season with salt and pepper. Transfer the sauce to a small bowl and keep warm.
Heat a grill pan. Rub the salmon with the olive oil; season with salt and pepper. Grill skin side down over moderate heat, turning once, until browned and just cooked through, 10 to 12 minutes. Spoon the mashed peas onto plates and top with the salmon, skin side up. Spoon the tarragon-butter sauce over the salmon and serve.