Combine buttermilk, egg, paprika, black pepper, garlic powder, onion powder, and salt in a large bowl.
Add chicken strips and mix well until evenly coated. Refrigerate for at least 4 hours and up to 24 hours.
In a large bowl, combine the flour, cornstarch, pepper, garlic powder, onion powder, paprika, and salt. Whisk until well blended. Pour in 3 tablespoons of the buttermilk marinade and stir with a fork until the mixture is evenly lumpy.
Working with one piece at a time, remove the chicken from the marinade, allowing excess to drip back into the bowl. Toss the chicken in the breading mixture, pressing down so that it sticks all over. Transfer to a baking sheet while you do the rest.
Heat about 1 inch of oil to 350°F. Fry a few strips at a time for 2-3 minutes on each side until they turn golden. Adjust the heat as needed (if they're browning too quickly, lower the heat). Transfer to a baking sheet lined with paper towels to drain excess oil.
Buttermilk: Substitute with a vinegar-milk mixture. Combine 1 tablespoon of vinegar with milk to make 1 cup.Storage: Leftovers can be stored in an air-tight container in the refrigerator for up to 5 days. To re-crisp, bake at 350°F for 10 minutes or air-fry at 400°F for 3 minutes, flipping once in between.Freezing: You can freeze the cooked chicken tenders for up to 3 months. To reheat, bake in a 350°F oven for 20-25 minutes, flipping them halfway through.