How to Make It
Pour oil to a depth of 1/2 inch into a large cast-iron skillet. Heat oil over medium-high to 325°F. (Closely watch the temperature, adjusting heat as necessary to maintain 325°F.)
Slice tomatoes into 1/4- to 1/2-inch-thick slices. (You should get 4 to 5 slices per tomato.) Place cornstarch in a wide, shallow dish. In a second wide, shallow dish, whisk together eggs, buttermilk, and 1/2 teaspoon kosher salt. In a third wide, shallow dish, stir together cornmeal, black pepper, cayenne pepper, and remaining 1 1/2 teaspoons kosher salt. Working in batches, dredge tomato slices in cornstarch, shaking off excess; dip in egg mixture, and dredge in cornmeal mixture, patting cornmeal coating onto slices. Place breaded slices on a parchment paper–lined baking sheet.
Working in batches, fry tomato slices (about 3 to 5 slices at a time) until golden brown and crispy, 3 to 4 minutes, flipping halfway through frying. Place on a baking sheet lined with paper towels, and sprinkle with sea salt.