Step 1Place the egg yolk in a medium-sized bowl, then whisk in the mustard and vinegar. Slowly whisk in the oil, in a thin stream, forming an emulsion. Stir in the hard-cooked eggs, capers, anchovies, parsley, tarragon and salt. Adjust with water if too thick. Set aside. This makes 1 1/2 cups sauce.
Step 1Bring a large pot of salted water to boil. Add the peas to the boiling water and blanch until the peas are just tender, about 1 minute. Using a long-handled strainer or slotted spoon, remove the peas from the boiling water and immediately place them in an ice bath, then drain them and set aside. Using the same pot of boiling water, repeat for the garbanzo beans; cook until just tender, about 1 to 2 minutes. Place them in an ice bath, drain and set aside. Then place the fava beans in the boiling water and cook 30 seconds to 1 minute. Put them in an ice bath and drain. Break the outer skin of each bean and squeeze the bean out of its skin. Set aside.
Step 2Clean the corn of all husk and silk. Cook the corn (on the cob) in simmering salted water for about 10 minutes, or until tender but crisp. Remove the cooked corn and allow to cool to room temperature, about 10 minutes. Cut the kernels from the cob and set aside.
Step 3Heat the oven to 350 degrees. Rinse the crabs under cold, running water and pat dry with a paper towel. Season the crabs with salt and cayenne pepper (about 1/8 teaspoon salt and a small pinch of cayenne per crab). Brush the top side of the crab with buttermilk. Then lay the brushed side in the cream of wheat. Crust only the top side.
Step 4To cook the crabs, work in two batches or with two 10-inch heavy-bottomed saute pans or skillets (you don't want to crowd the pan). Heat 2 tablespoons of the canola oil for each batch over high heat until it starts to smoke. Add half of the crabs, crust side down, to each pan. Immediately place the pan in the oven. Cook for about 4 minutes until the crust is golden brown, then flip the crabs and cook for an additional 3 minutes or until done.
Step 5While the crabs cook, warm the vegetables. Melt the butter in a large skillet over medium-low heat. Add the corn, peas, garbanzo beans and fava beans and warm through. Don't allow the butter to brown. Season with salt and pepper.
Step 6Divide the succotash between four plates. Place two cooked crabs on top of each. Top each crab with a tablespoon of the sauce gribiche.