How to Make It
Preheat the oven to 400°. Pour the milk into a large shallow dish and season with 2 teaspoons of salt and 1/2 teaspoon of pepper. Put the crabs in the milk and let marinate for about 10 minutes.
Slice the fennel very thinly on a mandoline. Transfer the fennel to a bowl and sprinkle generously with salt. Toss with 1 1/2 tablespoons of the lemon juice and refrigerate until ready to use.
In a small bowl, mix the remaining 1 1/2 tablespoons of lemon juice with the olive oil, Pernod, lime juice and sugar. Season with salt and pepper.
Heat 3 tablespoons of the vegetable oil in a large skillet. One by one, lift 4 of the crabs out of the milk and dredge them in flour, shaking off the excess. When the oil is almost smoking, fry the crabs over moderately high heat, top shell side down, until browned and crisp on the bottom, about 3 minutes. Turn the crabs and cook until crisp on the second side, about 2 minutes longer. Transfer the crabs to a rimmed baking sheet. Discard the oil and carefully wipe the skillet clean. Heat the remaining 3 tablespoons of vegetable oil in the pan. Flour and fry the remaining crabs, then transfer them to the baking sheet. Keep the crabs hot in the oven while you prepare the salad.
Squeeze the fennel dry. In a large bowl, combine the mesclun with the fennel and toss with the vinaigrette. Mound the salad on plates, top each salad with 2 crabs and serve.