If you're starting with raw chicken, season the breasts lightly and roast them at 400°F for about 25 minutes, or until they hit 160°F internally. Let the chicken rest and cool completely before dicing it. Skipping this cooling step can make your dressing go watery fast.
In a large bowl, combine the mayonnaise, sour cream, honey, lemon juice, apple cider vinegar, basil, rosemary, salt, and pepper. Whisk everything until it's fully smooth and well blended. Taste it here and adjust the seasoning if needed before moving on.
Add your diced chicken, celery, grapes, and toasted almonds directly into the bowl with the dressing. Gently fold everything together until the chicken and add-ins are evenly coated. Be careful not to overmix, or the grapes can start to break down.
Cover the bowl and refrigerate the chicken salad for at least 30 minutes before serving. This resting time lets the flavors settle and deepen, which makes a noticeable difference in taste. It also firms the texture up, making it much easier to scoop or spread.