White meat can dry out after a long haul in the slow cooker, so we opt for bone-in thighs to guarantee optimal flavor and succulence. Make prep easier with prepeeled garlic, and pretty-up the platter with lemon slices and thyme sprigs.
Coat bottom and sides of a 6-quart slow cooker with cooking spray.
Combine stock, wine, flour, butter, and 1 tablespoon lemon juice in a medium bowl, stirring with a whisk; pour mixture into slow cooker. Sprinkle chicken thighs evenly with 3/4 teaspoon salt and 1/4 teaspoon pepper. Place thighs in slow cooker, skin side down. Arrange potatoes, garlic, and thyme over chicken in slow cooker. Sprinkle 1/2 teaspoon salt and 1/4 teaspoon pepper evenly over garlic and potatoes. Cover slow cooker; cook on LOW for 8 hours.
Transfer chicken to a platter. Transfer potatoes and garlic to platter with a slotted spoon; discard thyme sprigs. Sprinkle chicken and potatoes evenly with remaining 1/2 teaspoon salt, remaining 1 tablespoon lemon juice, and parsley. Strain cooking liquid from slow cooker through a sieve into a liquid measuring cup; let stand 3 minutes. Discard any fat that rises to top of liquid. Serve jus with chicken, potatoes, and garlic cloves.