Combine eggs and buttermilk in a large bowl and whisk together. Submerge all chicken pieces in the buttermilk mixture, ensuring each piece is fully covered. Marinate in the refrigerator for at least 30 minutes, or up to 4 hours for maximum tenderness.

Pour flour into a shallow bowl and add paprika, garlic powder, onion powder, black pepper, salt, and cayenne pepper if using. Whisk everything together thoroughly to distribute the spices evenly throughout the flour.

Remove chicken pieces from buttermilk one at a time, letting excess liquid drip off. Dredge each piece thoroughly in the seasoned flour, coating all sides and crevices. Press the flour gently onto the chicken to help it adhere. Shake off excess flour and place coated pieces on a plate.

Pour vegetable oil into a large deep skillet or Dutch oven to a depth of about 2 inches. Heat over medium-high heat until it reaches 350 degrees Fahrenheit, using a thermometer to ensure accurate temperature.

Working in batches to avoid crowding, carefully place coated chicken pieces into hot oil. Drumsticks and thighs take about 12 to 15 minutes to cook, while breasts take about 10 to 12 minutes. Avoid moving pieces around; let them sit for a few minutes per side for even browning. Chicken is done when a meat thermometer inserted into the thickest part reads 165 degrees Fahrenheit.

Transfer fried chicken to a plate lined with paper towels to drain excess oil. Let rest for a few minutes before serving to maintain crispiness and retain juices.

Start with a bed of shredded lettuce on your plate. Arrange sliced tomato and red onion on top. Add french fries to one side. Top everything with hot fried chicken pieces and serve immediately.