Louisiana Deviled Crab Cakes

Name: Louisiana Deviled Crab Cakes
Ingredients: 1/4 cup finely chopped onion; 1/4 cup finely chopped green bell pepper; 3 tablespoons finely chopped celery; 3 tablespoons unsalted butter; 1 large egg; 1 tablespoon sour cream; 1/2 teaspoon dry mustard; 1/2 teaspoon Worcestershire sauce; 3/4 teaspoon cayenne; 3/4 teaspoon salt; 2 tablespoons thinly sliced scallion greens; 16 saltines, finely ground; 1/2 lb jumbo lump crabmeat, picked over; 1 tablespoon vegetable oil; Accompaniments: tartar sauce and lemon wedges