Add enough of the oil to a large sturdy skillet (ie, cast-iron) to fill it to about 1/2-inch to 1-inch in depth. Heat over medium-high heat to 350°F.: The moment the oil starts to shimmer you will notice a faint, warm scent of toasted fat that signals readiness. As the skillet warms, tiny ripples will cross the oil surface, and occasional wisps of steam may rise. Using a thermometer is invaluable, because maintaining about 350°F ensures the crust crisps quickly without absorbing excess oil. One common mistake is rushing the heat, which causes uneven browning and greasy texture. If you see the oil smoking, reduce the heat immediately to prevent burning; if the oil is too cool, the coating soaks up oil and becomes heavy.
Meanwhile, set up a dredging station with three small to medium-sized baking pans or bowls. Place the flour in the first pan, buttermilk in the second, and mix in the third pan the cornmeal, breadcrumbs, paprika, cayenne, salt, and pepper.: A well organized station lets you move smoothly from one bowl to the next, and you will be able to feel the rhythm as each slice passes through layers. The dry mixture should look cohesive and have a slightly speckled appearance from the paprika and cayenne pepper . I often tap the cornmeal mixture gently to level it, so the breadcrumbs do not clump. A typical oversight is crowding the pans, which leads to clumsy transfers and uneven coating; leave enough space so each slice can be handled comfortably.
Place the sliced tomatoes first in the flour, flipping to coat and cover. Shake off excess and then lower into the buttermilk. Shake off excess and then add to the cornmeal/breadcrumb mixture. Use your fingers to help the breading adhere to the tomato. It's okay if the tomato is not 100% coated with the breading.: You will notice the flour attaching like a thin veil, and when the slices meet the buttermilk they should glisten slightly. Press the slices gently into the dry mix so the cornmeal and breadcrumbs cling, and the surface takes on a textured, pebbled look. This tactile step is key for adhesion, and the small imperfections in coating are normal. Avoid overhandling, which can squeeze juices out of the tomato , making it soggy when fried.
Working in batches, carefully add the tomatoes to the hot oil. Cook them for about 2 minutes, and then use a fork and metal spatula or tongs to carefully flip the tomatoes over. Fry for another couple of minutes, or until they are golden brown. Transfer to a plate lined with paper towels. Repeat with remaining tomatoes.: As each slice hits the oil you should hear a lively, steady sizzle, like a soft crackling applause. The sound will mellow slightly as the moisture in the tomato escapes and the crust sets. Look for an even golden brown color forming at the edges, and an aroma of toasted breadcrumbs will spread through the kitchen. Flipping gently prevents the crust from tearing; a loud pop or excessive bubbling can mean the oil is too hot. Drain on paper towels to remove excess oil; overcrowding the pan causes uneven color and soggy texture, so work in small batches.
Serve at once with homemade ranch dressing (or your favorite dipping sauce).: The contrast between the warm, crunchy slices and the chilled, tangy Ranch dressing is immediate and delightful, and you will notice how the dressing softens the spicy notes from the cayenne pepper . Serve on a warm platter so the tomatoes stay crisp longer, and offer extra napkins because the exterior can be slightly oily right out of the pan. A common misstep is letting the fried slices sit too long, which causes the crust to lose its crispness; serve promptly for the best texture.