If serving, make rémoulade sauce. Whisk together all sauce ingredients in a small bowl until well-combined and smooth. Let sit for one hour so flavors meld while you prepare the tomatoes. (Cover and refrigerate any leftover sauce.)
Pre-heat oven to 200º and fit a sheet pan with wire rack, set aside.
In a wide bowl or pie plate, combine flour, cornmeal and seasonings. In another small bowl, combine buttermilk with a few shakes of hot sauce and a little salt and pepper. Dip green tomato slice in buttermilk mixture, shake off excess, then dredge in cornmeal-flour mixture until well-coated. Repeat and put tomato slices on a plate.
Heat oil in a large cast iron pan, about a ½-inch high. Add the butter and mix in, it gives flavor and helps with browning. When hot, but not smoking, add tomato slices to skillet, and working in batches, fry until golden, about 3-4 minutes a side. Transfer to paper towel-lined plate to drain and sprinkle with salt while hot. Transfer fried slices to sheet pan with rack and keep warm in oven while continuing to fry remaining slices.
Serve hot green tomatoes with lemon wedges, Louisiana hot sauce and/or rémoulade sauce. Enjoy!