Season the salmon with salt and pepper. Heat a large skillet over medium-high heat. Spread some flour on a plate. Lightly dredge the salmon in the flour on all sides, tapping off the excess. When the skillet is hot, add the vegetable oil. Add the salmon, and cook, turning once, until almost cooked through, 2 to 3 minutes per side, depending on the thickness of the fillets. The fish should still be rare in the center, because it will cook more in the sauce. Remove to a plate.

Carefully discard the oil from the pan. Return the pan to medium heat, and add the butter. Once it has melted, add the wine, and reduce by half, about 2 minutes. Add the fish stock and lemon juice, and bring to a simmer. Simmer until it’s reduced by about a quarter and slightly thickened, about 2 minutes.

Add the cream, and simmer for 1 minute. Whisk in the mustard, return the salmon to the sauce, and simmer until the fish is just done and heated through and the sauce coats the back of a spoon, about 2 minutes. With a spatula, carefully transfer the fillets to serving plates. Strain the sauce, and spoon a little over each fillet.