Heat oil in a deep-fryer to 360 degrees F (182 degrees C).
Whisk flour, corn flakes, baking powder, salt, pepper, and sugar together in a shallow bowl. Pour milk into a separate shallow bowl.
Gently press one tomato slice into the flour mixture to coat on both sides and shake off any excess. Dip into milk, then press again in flour mixture. Repeat with remaining tomato slices. Place breaded tomato slices in a single layer on a plate while breading the rest; do not stack.
Cook each breaded tomato slice in the hot oil until golden brown, about 3 minutes per side. Remove to a paper towel to drain and cool.
Use a deep fryer for this recipe; regular frying pans are too shallow and loosened breading will burn easily, causing oil to often need to be changed.
Make sure to keep the fried green tomatoes from soaking up too much oil by keeping the deep frying temperature at 360 degrees or slightly higher, not crowding the breaded green tomato slices while frying (can cause oil temperature to drop), and turning each frying slice only one time.
The nutrition data for this recipe includes the full amount of the breading ingredients. The actual amount of the breading consumed will vary. We have determined the nutritional value of oil for frying based on a retention value of 10% after cooking. The exact amount will vary depending on cooking time and temperature, ingredient density, and the specific type of oil used.