In a large bowl, mix buttermilk, paprika, garlic powder, onion powder, salt, and black pepper.
Add the chicken breasts and coat well. Cover and refrigerate for at least 1 hour, or overnight for deeper flavor.
In a shallow dish, whisk together the eggs, milk, and vanilla extract.
Heat a large skillet or griddle over medium heat and melt 1 tablespoon butter.
Dip each bread slice into the egg mixture, coating both sides, then place on the hot skillet.
Cook each slice for 2 to 3 minutes per side, until golden brown. Repeat with the remaining bread, adding more butter as needed.
Remove the chicken from the marinade. Dredge each piece in flour, dip back into the marinade, then coat with breadcrumbs.
Heat oil in a skillet over medium-high heat. Fry the chicken for 5 to 7 minutes per side, or until golden, crisp, and cooked through.
Transfer the chicken to a paper towel-lined plate.
To assemble the French Toast Fried Chicken Sandwich, place one slice of French toast on a plate, add fried chicken, then top with another slice of French toast.
Drizzle with maple syrup and finish with powdered sugar, fruit, or whipped cream if desired.
Serve hot.