How to Make It
In a small saucepan, boil the vinegar over moderately high heat until reduced by half. Transfer to a large heatproof bowl and let cool, then stir in the honey. Add the cabbage, onion and carrot, season with salt and black pepper and toss well. Let stand at room temperature for 15 minutes, stirring occasionally. Add the mayonnaise, 2 tablespoons of the mustard, the chives, parsley and cayenne and season again with salt and black pepper.
In a small bowl, combine the remaining 1 tablespoon of mustard with the crème fraîche
In 2 large skillets, cook the bacon over moderately high heat until crisp, about 6 minutes. Transfer to paper towels to drain. Reserve the bacon fat in the skillets.
Spread the flour on a large plate. Lightly dust the crabs with the flour. Warm the bacon fat over moderately high heat until shimmering. Add the crabs to the skillets and cook, turning once, until golden, about 8 minutes. Drain on paper towels and season lightly with salt.
Arrange the bacon on the bottom half of the baguette and mound the slaw on top. Arrange the fried crabs on the sandwich as close together as possible and drizzle with the mustard crème fraîche. Close the sandwich and use a serrated knife to carefully cut it into 10 pieces. Serve immediately, with lemon wedges for seasoning.