Place the potatoes in a pot, cover with a generous amount of cold water and boil until almost tender. Add the romanesco and cook three minutes more, or until it and potatoes are tender. Drain well, cool vegetables in cold water, and drain well again.
Preheat the oven to 425°F. Using a sharp knife, carefully cut the crab legs widthwise, into 2" to 4” long pieces. Use kitchen scissors to cut off the top part of the shell on one side of each piece to expose the crabmeat.
Arrange the crab pieces, exposed meat side up, and the potatoes and romanesco florets on a sided baking sheet. Combine remaining ingredients, except lemon slices, in a small bowl. Drizzle this mixture over the crab and vegetables. Bake 10 to 12 minutes, or until the crab and vegetables are steaming hot. Garnish with lemon slices, set the pan on the dining table and dig in.
Note: Romanesco is a member of the brassica family and is related to plants such as cauliflower, why it's also known as green cauliflower. Learn how to cut into florets by going to thriftyfoods.com and searching romanesco. If you didn’t want to use wine in this recipe, replace with (gluten-free) chicken or fish stock.