This decadent appetizer gets even more flourish from a tangy lime-avocado puree and broccoli rabe flower garnish.
Insert a teaspoon between flesh and peel of one lime half; scoop out flesh in one whole piece. Repeat with remaining lime halves; set all lime cups aside. Place all flesh in a fine sieve, and extract lime juice; discard solids. Set 1 tablespoon lime juice aside, and reserve the remaining juice for another use.
In a small saute pan, melt 1 tablespoon butter over medium-low heat. Add shallots and garlic; cook until translucent, about 7 minutes. Remove pan from heat; transfer shallot mixture to a large bowl.
Tear bread into small pieces; place in a small bowl. Add milk, and let stand until bread is soaked through, about 5 minutes. Squeeze out all the milk from the bread, and add bread to shallot mixture.
Heat oven to 250 degrees. Add crabmeat, egg, mustard, 1 tablespoon lime juice, cayenne, parsley, and marjoram to shallot mixture. Season with salt and black pepper. Mix until well combined. Shape mixture into twelve 2-inch-round patties. Pour breadcrumbs into a bowl; coat crab cakes.
Melt 1 tablespoon butter and 1 tablespoon canola oil in a large skillet set over medium heat. Add six crab cakes; cook until golden brown and heated through, about 2 minutes on each side. Transfer crab cakes to a baking pan, and place pan in oven to keep warm. Wipe out skillet, and cook remaining six crab cakes with the remaining tablespoon butter and oil.
To serve, toss the mizuna and broccoli-rabe flowers with citrus dressing, and divide among 12 plates. Spoon the lime-avocado puree into the lime cups, and place each cup on a plate. Place one crab cake on each plate; garnish with tomatoes. Drizzle cilantro oil over the tomatoes and around each plate.