4 bone-in chicken breast halves (10 to 12 ounces each) skin removed
2 tablespoons reduced-fat sour cream
1 tablespoon cider vinegar
3 slices (1 ounce each) white sandwich bread torn into large pieces
2 teaspoons olive oil
3/4 teaspoon Herbes de Provence
1 bag (5 ounces) baby spinach
1 medium red apple halved, cored, and thinly sliced
1 cup seedless red grapes halved
Make marinade: In a large bowl, whisk together 2 cups buttermilk, 3 tablespoons honey, garlic, 2 teaspoons coarse salt, and 1/2 teaspoon pepper. Place chicken in a re-sealable plastic bag (or baking dish); add marinade and seal (or cover). Refrigerate at least 2 hours or up to 1 day.
Make salad dressing: In a jar, combine remaining 1/4 cup buttermilk, sour cream, vinegar, and 1 teaspoon honey; season generously with salt and pepper. Shake vigorously to combine. Refrigerate.
Preheat oven to 425 degrees. In a food processor, pulse bread, oil, and Herbes de Provence until fine crumbs form; season generously with salt and pepper (you should have about 1 1/2 cups).
Line a rimmed baking sheet with foil. Lift chicken from marinade, letting excess drip off (discard remaining marinade). Place chicken on foil, bone side down; sprinkle with breadcrumbs, patting them on lightly. Bake until crumbs are browned and chicken is cooked through, 30 to 40 minutes.
Meanwhile, in a large bowl, combine spinach, apple, and grapes. Add dressing and toss. Serve salad with chicken.