Combine buttermilk, hot sauce, lemon juice, and minced garlic in a bowl and submerge the catfish. Cover with plastic wrap and let rest in the fridge for 30 minutes. Remove from the brine, rinse and thoroughly pat dry with a paper towel.
Cut the catfish into desired size, then cover with mustard, old bay, lemon pepper, garlic powder, and onion powder, seasoned salt, and black pepper. Toss together to ensure everything is coated in the seasoning.
Combine ingredients for the dredge in a bowl - cornmeal, all purpose flour, cornstarch, parsley, cajun seasoning, and baking powder.
In a separate bowl, combine the ingredients for the wet batter - whisk together eggs, buttermilk, hot sauce, and Worcestershire sauce.
Dip catfish in the seasoned cornmeal mixture, then the egg mixture, and then back in the dredge. Make sure to pat the dredge into the fish, ensuring the catfish fillets are fully coated. Place onto a wire rack to set while the oil is heating.
Add vegetable oil to a large cast iron skillet or pot over medium-high heat. Heat the oil to 350-375 degrees F. Use a candy thermometer to ensure the temperature of the oil is correct.
Add 1-2 fillets to the skillet at a time and cook for 3-5 minutes per side, until golden brown. Remove from the oil and place onto a paper towel-lined plate to remove any excess oil.
Notes
Don't let the catfish marinate any longer than 2 hours. The acid in the buttermilk will make the catfish mushy if you let it sit too long.
After soaking in the buttermilk marinade, Pat the fish dry with a paper towel. Excess moisture will make the coating soggy and will cause the breading to fall off when frying in the hot oil.
Use a candy thermometer to monitor the oil's temperature. Frying at the right temperature is key to getting crispy fried fish! The oil temperature should be between 350-375 degrees F.
Don’t crowd the pan. Fry in batches so the oil temperature stays where we need it to be.