1. Heat oil in medium saucepan over medium heat until shimmering but not smoking; add shallot and cook, stirring frequently, until softened and beginning to color, about 1 1/2 minutes. Add orange juice and vinegar, increase heat to high, and bring to boil; boil until reduced to 3/4 cup, 4 to 6 minutes. Add heavy cream and continue to cook until slightly reduced, about 1 minute. Remove saucepan from burner, whisk in butter and tarragon until combined; season to taste with salt and pepper. Cover to keep warm; set aside, stirring once after about 1 minute.

2. To serve, stir sauce to recombine and spoon 1/2 cup over fish. Serve immediately with orange wedges, passing remaining sauce separately.

Makes about 1 cup