For the toast rounds: Preheat oven to 350°F. Slice the French baguette into 1/4-inch rounds. Arrange slices on a baking pan and brush lightly with olive oil. Toast until just light brown, 5 to 7 minutes. Turn and brush the other side lightly with olive oil, toast again until golden and set aside.
For the crab toast: Remove and discard any cartilage from the backfin meat. Set aside. In a small mixing bowl whisk together mayonnaise, Creole mustard, lemon juice, hot sauce, celery, green onions, seafood seasoning and lemon zest. Gently fold in lumps of fresh crab. Season the dip with ground black pepper. Spoon onto toasted French bread rounds lined with celery leaves. Sprinkle on chopped parsley.
Note: Fresh crab can be particularly difficult to find if you’re landlocked. It’s even difficult to find a year-round supply along the Gulf Coast, where blue crab is commercially available year-round. That’s why crab processors also purchase pasteurized crabmeat. Pasteurization is a process wherein fresh crabmeat is cooked and picked, and then sealed into airtight cans and heated to a temperature of about 185°F, then cooled quickly.