Cracked Crab with Horseradish Mayonnaise

To make the horseradish mayonnaise, in a small bowl, whisk together the egg yolk, mustard and 1 Tbs. of the olive oil until an emulsion forms. Combine the remaining olive oil and the vegetable oil in a cup with a spout. Drop by drop at first and whisking constantly, gradually add the oil mixture to the emulsion. Stir in the garlic, the 1 1/2 Tbs. lemon juice and the horseradish. Season with salt and pepper and add more lemon juice, if needed. Whisking constantly, add the warm water to thin the mayonnaise slightly. Cover and refrigerate until ready to serve.

To prepare the crabs, in a large pot, bring the water to a boil over high heat. Once it boils, add the salt and the crabs, immersing them completely. Boil until the crabs are cooked and the shells are red, about 12 minutes. Using tongs, transfer the crabs to a plate and let cool slightly.

Working with 1 crab at a time, place the crab on its back. Pull off the small triangular apron-shaped shell flap and discard. Turn the crab over and lift up and snap off the large top shell and discard. Remove the dark gray intestines and the feather-shaped white spongy gills from the body and discard. Rinse the body well. Using a large, heavy knife, cut the body in half from the head to the tail. Cut each half crosswise into thirds. Using a lobster cracker or a mallet, crack the claws and legs. If the crabs have cooled, warm them on a steamer rack over boiling water for 5 to 7 minutes.

To serve, arrange the crabs on a platter and serve with small forks or lobster picks for extracting the meat. Offer the horseradish mayonnaise on the side.