Combine 1 cup buttermilk, 1 tablespoon Hidden Valley Original Ranch seasoning, and 1/4 teaspoon pepper in a freezer-size plastic bag to make the marinade.
Add the 10 chicken tenderloins to the bag, seal, and refrigerate to marinate for 2–8 hours.
While the chicken marinates, whisk together 1/4 cup sour cream, 1/4 cup mayonnaise, 1 tablespoon milk, and 2 teaspoons Hidden Valley Original Ranch seasoning in a medium bowl; refrigerate until serving.
Preheat the oven to 400°F (200°C). Line a baking sheet with a rack and lightly spray the rack with nonstick cooking spray.
Crush the Ritz and cheese crackers in a food processor or by hand until they resemble coarse crumbs (about panko size).
In a large bowl, combine the crushed Ritz crackers, crushed cheese crackers, 1/2 cup panko, 1/2 cup grated sharp cheddar, 2 tablespoons dry ranch seasoning, 1/2 teaspoon paprika, 1/4 teaspoon salt, and a pinch of cayenne (if using).
Remove one chicken tenderloin from the marinade, letting excess drip off or patting lightly with a paper towel, then press it firmly into the breading mixture to coat on all sides.
Place the breaded tender on the prepared rack; lightly spray the top with nonstick cooking spray. Repeat with remaining tenders.
Bake at 400°F for 12–18 minutes, until the chicken reaches an internal temperature of 165°F and is cooked through.
Optional: broil a minute or two at the end to achieve extra crispiness, watching carefully to prevent burning.
Serve the baked cheddar ranch chicken tenders warm with the chilled ranch dip.
