Preheat the oven to 425 degrees F. Line a large baking sheet with parchment paper. Set in the salmon. Brush the fish with the oil and lemon juice; season with salt and pepper. Bake for 15 minutes, or until just cooked through.
While the fish cooks, place the wine in a medium pot set over medium heat. Bring to a simmer and reduce by half. Add the cream and simmer until lightly thickened. Whisk in the mustard and tarragon; season with salt and pepper. Plate the salmon, top with sauce and serve.
Note: If desired, you could use dried tarragon in the sauce. If you do, add 1 tsp. of it to the wine before reducing it.