Grilled Cheddar and Fennel Sandwiches with Curry Mayo

Cook shallot and curry powder in oil in a 12-inch heavy nonstick skillet over moderate heat, stirring, 2 minutes, then transfer to a small bowl and stir in mayonnaise and lemon juice. Wipe skillet clean and set aside. Cut 16 (1/4-inch-thick) diagonal slices (about 6 inches long) from baguette. Spread 1 side of each slice with butter, then turn over and spread opposite side with curry mayonnaise. Cut cheese into thin slices no wider than bread slices. Divide cheese among 8 slices of bread, then top with fennel and remaining slices of bread, buttered sides up. Heat skillet over moderate heat until hot, then cook sandwiches in 2 batches, turning over once and pressing occasionally, until browned and cheese is melted, about 7 minutes per batch.