Make the remoulade sauce: In a medium bowl, whisk together all the ingredients. Taste, and adjust seasonings if needed. Refrigerate until ready to use.
Using a serrated knife, cut tomatoes into 3/8″ thick slices (that’s between 1/4 and 1/2-inch thick.) Sprinkle both sides with coarse salt. Let stand for 30 minutes to draw out the moisture (this helps the breading stick better.) Gently pat dry with paper towels.
Set up the breading station with 3 separate shallow dishes (pie plates are great!):
1st dish: whisk together the flour, garlic powder, onion powder, and smoked paprika.
2nd dish: whisk together the buttermilk, egg white, and hot sauce.
3rd dish: combine the breadcrumbs and cornmeal.
Fit a wire rack inside a rimmed baking sheet. Dip each tomato slice in the flour mixture (shake off excess), followed by the buttermilk mixture, and finally the cornmeal mixture (press gently to adhere.)
Place the breaded tomato slices on the rack in a single layer. Let sit while you heat up the oil – this allows time for the coating to set.
In a large cast iron skillet, warm oil over medium-high heat until it reaches 350 degrees F and shimmering. (The oil should sizzle immediately if you sprinkle water into it.)
Starting with the tomatoes that were breaded first, carefully add 3 to 4 to the hot skillet, taking care not to over-crowd them. Fry until golden-brown, 3 to 5 minutes per side, regulating the heat if the oil gets too hot.
Transfer the fried tomatoes to a paper towel-lined plate to drain. Fry the remaining tomato slices, replacing the oil if necessary.
Serve immediately with the remoulade sauce.