In a microwave-safe bowl, add potatoes, onions, carrots, and celery. Cook in microwave for 4 minutes, to soften.
To make the sauce: melt butter in a large saucepan. Add garlic and cook, stirring frequently, until fragrant, about 1 minute. Whisk in flour until lightly browned, about 1-2 minutes. Gradually whisk in chicken broth and thyme, Cook, whisking constantly, until the sauce begins to thicken, about 3-5 minutes.
Lightly coat the inside of crock-pot with nonstick spray. Season chicken thigh pieces with a pinch of salt and pepper, to taste. Place chicken pieces into crock-pot. Add softened potatoes, onion, carrots, and celery. Stir in chicken stock mixture and bay leaf. Cover and cook on low heat for 3-4 hours or cook on high for 1-2 hours. Add peas. Cover and keep warm for an additional 5 minutes.
Prepare biscuits according to package instructions. Serve chicken topped with 1 biscuit, if desired.