We developed this recipe with Hidden Valley Original Ranch Seasoning.
Adjust oven rack to middle position and heat oven to 400 degrees. Whisk 6 tablespoons mayonnaise, milk, dill, 1 tablespoon ranch seasoning, and cayenne together in bowl; refrigerate sauce. Combine panko, 2 tablespoons butter, and 1 teaspoon ranch seasoning in second bowl and microwave until golden brown, about 2 minutes, stirring occasionally. Toss broccoli, ½ teaspoon salt, ¼ teaspoon pepper, and remaining 4 tablespoons butter together on rimmed baking sheet. Roast for 10 minutes.
Meanwhile, pat chicken dry with paper towels and sprinkle all over with remaining 1 teaspoon salt and ½ teaspoon pepper. Combine remaining 2 tablespoons mayonnaise and 1 teaspoon ranch seasoning in bowl, then spread over tops of chicken. Sprinkle tops of chicken with panko mixture.
Remove sheet from oven. Push broccoli to 1 half of sheet. Arrange chicken on empty half. Roast until chicken registers 160 degrees and broccoli is crisp-tender, about 15 minutes. Serve with sauce.
