Add chicken, chicken broth, white wine, 1 teaspoon rosemary, tarragon, thyme, 1 teaspoon salt, pepper, carrots, celery, and leeks to slow cooker. Secure lid and set to low for 6 hours.
Prepare biscuits in last 30 minutes of the cook time. (You can use refrigerator biscuits, the butter swim biscuit recipes I have linked in the post, or whatever your favorite biscuit recipe).
Preheat oven to Broil setting. Place a cooking rack on a parchment paper covered baking sheet. Remove chicken pieces from slow cooker and lay out on the cooking rack. Cook for 3 minutes on each side under broiler.
In a sauce pan over medium heat, add butter. Once melted whisk in flour and cook for 2 minutes. Ladle 2 cups of chicken stock (from the slow cooker while trying to only get liquid) into sauce pan and whisk together. Cook for 3 minutes and whisk in heavy cream, remaining salt and remaining rosemary. Reduce heat to medium-low.
Remove 2 cups of veggies and liquid from the slow cooker to a bowl. Using an immersion blender to blitz until smooth. Then stir into cream sauce.
Add 2 biscuits and 1 or 2 pieces of chicken to a plate. Ladle cream sauce over top.