For the crab cakes: Gently pick through the crab meat to remove any shell pieces. In a bowl, combine the crab and panko breadcrumbs and mix gently. In a separate bowl, add the mayonnaise, parsley, mustard, seafood seasoning, hot sauce, Worcestershire sauce and egg and whisk to combine.
Pour the crab cake base over the crab meat and mix gently by hand, trying to keep the pieces of crab together. Allow the crab cake mix to rest for 45 minutes in the refrigerator. Divide the crab cake mix into 12 portions and form into cakes.
Heat a skillet over high heat. Add 2 tablespoons of the oil and sear half of the crab cakes until golden brown, 2 to 3 minutes per side. Let the first batch rest while you cook the second batch with the remaining 2 tablespoons oil.
For the tartar sauce: Combine the mayonnaise, buttermilk, relish and capers in a bowl and whisk. Season with salt and pepper.
For the tomato relish: Heat the oil in a medium saucepan. Add the garlic and saute until softened, 1 to 2 minutes. Add the tomatoes and tarragon and cook until warmed through, 3 to 4 minutes. Add the vinegar and sugar and bring to a boil. Cook until the liquid is reduced to a syrup, 10 to 15 minutes. Season with salt and pepper.
For plating: Smear about 2 tablespoons of the tartar sauce on a plate. Shingle 2 crab cakes on top of the tartar sauce and then top the crab cakes with 2 tablespoons of the tomato relish. Repeat with the remaining crab cakes, tartar sauce and tomato relish.