Melt butter with oil in a Dutch oven over medium heat. Add onion and next 4 ingredients; sauté 8 minutes or until tender.
Stir in flour and next 5 ingredients; cook 1 minute, stirring frequently. Add sherry and clam juice; stir until well blended. Stir in parsley and tarragon. Bring to a boil, reduce heat, and simmer, uncovered, 15 minutes or until reduced to 4 cups.
Pour mixture through a wire-mesh strainer into a separate bowl or pan, pressing on solids with a spatula; discard solids. Return soup to Dutch oven; stir in cream. Cook over medium heat 25 minutes or until soup is thickened. Add crabmeat; cook 3 to 5 minutes or until warmed through. Season to taste with salt and pepper.