Heat oil and butter in the pot.
Brown chicken pieces lightly.
Remove chicken and set aside.
Sauté onions, carrots, and celery.
Add garlic and cook briefly.
Stir in flour until coated.
Slowly add stock, stirring constantly.
Add milk, herbs, and seasoning.
Return chicken to the pot.
Simmer gently until thickened.
Prepare biscuit dough separately.
Drop biscuit portions onto stew.
Cover and cook until biscuits puff.
Uncover briefly to finish biscuits.