Pour buttermilk over catfish fillets and let them soak for about 15-20 minutes. Meanwhile, prepare the tartar sauce.
In a bowl, mix mayonnaise (olive oil version), minced garlic, minced onion, dill, sweet relish, and a squeeze of lemon juice. Add a pinch of salt and mix well. Adjust ingredients to taste.
In a separate bowl, combine cornmeal, salt, and pepper. You can also add your preferred seasoning (e.g., Creole seasoning) for extra flavor.
After marinating, remove catfish from buttermilk. Coat each fillet evenly with the cornmeal mixture.
Heat cooking oil in a pan to around 350-370°F (use a thermometer). Gently place the coated catfish fillets into the hot oil. Fry until the fillets are golden brown, approximately 4 minutes per side. Use a splatter guard if needed to reduce oil splattering.
Once fried, transfer the catfish to a paper towel-lined plate to absorb excess oil. Serve the fried catfish hot with the prepared tartar sauce on the side.
Garnish with lemon wedges and serve with your favorite sides. Enjoy your crispy and flavorful fried catfish!