Whisk together the flour and water in a shallow bowl until smooth. Season with hot sauce, salt, and pepper. Spread the cornmeal onto a plate and season with salt and pepper.
Pat the tomatoes dry with paper towels. Heat 1-inch of oil in a cast-iron pan over medium-high heat until it begins to shimmer. Season the tomatoes on both sides with salt and pepper. Dip each tomato into the batter and let the excess drip off. Dredge in the cornmeal and pat off the excess. Fry the tomatoes, in batches, until golden brown on both sides.
Spread both sides of the bread with some of the Remoulade Sauce. Top 1 side with a few slices of tomatoes, a few strips of bacon, and some watercress. Top with the other slice of bread, sauce-side down. Repeat to make 4 sandwiches.
Whisk together the yolks, lemon juice, vinegar until pale. Slowly drizzle in the canola oil until emulsified. Season with salt and pepper. Whisk in the mustard, cornichons, thyme, and season with salt and pepper. Refrigerate for at least 1 hour before serving to allow the flavors to meld.
*RAW EGG WARNING
Food Network Kitchens suggest caution in consuming raw and lightly-cooked eggs due to the risk of Salmonella or other food-borne illness. To reduce this risk, we recommend you use only fresh, properly-refrigerated, clean, grade A or AA eggs with intact shells, and avoid contact between the yolks or whites and the shell. For recipes that call for eggs that are raw or undercooked when the dish is served use shell eggs that have been treated to destroy Salmonella, by pasteurization or another approved method.