Slice ficelle lengthwise down the center of the top of the loaf. Be sure not to cut all the way through. Spread halves open.
Combine Dijon mustard and corn oil and whisk until emulsified. Add sherry wine vinegar. Whisk to combine.
Layer tomatoes in pocket of bread. Layer mozzarella on top of tomatoes. Grind pepper over top of sandwich.
Pour vinaigrette over tomatoes. Add basil leaves to top of sandwich. Cut sandwiches in sections.
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