Spray inside of pot with non stick spray. Pour liquid into bottom of pot.
Combine seasonings into a bowl and mix.
Use half of the softened butter and rub this under the skin of the breast. Rub half of the seasoning rub underneath too.
Sprinkle and rub remaining seasonings on the top of the breast.
Put into middle of pot. Cover and cook on low heat for 6 hours or until middle of thickest part of the meat reaches 165 degrees F.
If you want crispy skin preheat broiler, put on sheet pan and crisp for 5-10 minutes. If you have a larger air fryer you could spray top with olive oil spray and crisp in that at 400 for a few minutes.
To make gravy, melt remaining butter in a saucepan. Add drippings from slow cooker into pan. You can add more broth at this time depending on how much you want.
In a small bowl whisk together 3 tbsp cornstarch with some of your hot liquid until smooth. Pour this into pan and stir as it thickens. Add more this way until it is the consistency you want.