1. Make the remoulade: Mix the mustard, ketchup, Worcestershire sauce, garlic, lemon juice, paprika, white pepper, cayenne and sugar in a large bowl; season with salt. Whisk in the olive oil in a slow stream until blended. Whisk in the celery, parsley, onion, scallion, mayonnaise and hot sauce. Cover and refrigerate until ready to serve.
2. Prepare the shrimp: Bring 2 quarts water to a boil in a large pot. Add 3 tablespoons salt, the lemon slices, hot sauce, bay leaves, carrot and Worcestershire sauce; boil 10 to 15 minutes. Add the shrimp and return to a boil, then reduce the heat and simmer until the shrimp are opaque and just firm, 5 to 7 minutes. Drain the shrimp and run under cold water to stop the cooking. Discard the carrot, lemon slices and bay leaves. Cover the shrimp and refrigerate until cold.
3. Fry the tomatoes: Mix the cornmeal, 1/4 teaspoon salt and teaspoon black pepper in a shallow dish. Put the buttermilk in another shallow dish. Heat the vegetable oil in a large deep skillet over medium-high heat. Dip the tomato slices in the buttermilk, then coat with the cornmeal, shaking off the excess. Fry until golden brown, 1 to 2 minutes per side.
4. Place 2 fried tomato slices on each plate. Top with the shrimp and drizzle with the remoulade.
5. Photograph by Lisa Shin