How to Make It
In a large skillet, melt the butter in 2 tablespoons of the oil until the foam subsides. Season the crabs with salt and pepper and add them, top side down, to the skillet. Cook over high heat until crisp and browned, about 3 minutes. Turn; fry until golden and cooked through, about 2 minutes longer.
Meanwhile, in a large bowl, toss the nasturtiums with the remaining 1 tablespoon of oil. Add the vinegar and a generous pinch each of salt and pepper. Toss again, arrange the salad on 4 plates, set a crab on each and serve.