Clean and slice the mushrooms. Peel and slice the shallot. Peel the carrots, rinse, and dice them. Wash and slice the leek white.

Heat the butter and 1 tablespoon of oil in a large skillet. Sauté the shallot and vegetables for 5 minutes, stirring. Add the white wine and fish stock, season lightly with salt and pepper, and simmer for 10 minutes.

Stir in the cream and tarragon, and cook for 5 more minutes. In a separate pan, heat the remaining oil and sear the scallops for 30 seconds on each side. Add the scallops to the skillet, gently mix, cook for 1 more minute, and serve.