3/4 pound salmon steak (1 1/4 inches thick)
Salt and pepper to taste
1/3 cup tawny port (as dry as possible)
1/4 cup firmly packed, fresh tarragon leaves (no stems)
1 large shallot, minced
1/4 cup beef stock
1 stick (1/2 cup) cold butter
1 teaspoon vegetable oil
Coarse salt for sprinkling the salmon