In the pressure cooker, heat oil over medium heat. Add chicken in batches and cook until browned. Set aside.
Drain off all but 1 Tbsp of fat. Add onion and garlic; sauté for 2 minutes. Stir in flour, potatoes, celery, carrots, parsnip and turnip. Gradually stir in stock and wine. Add bay leaf. Bring to a boil and return chicken and any accumulated juices to cooker.
Lock the lid in place and bring the cooker up to full pressure over high heat. Reduce heat to medium-low, just to maintain even pressure, and cook for 12 minutes. Remove from heat and release pressure quickly.
Discard bay leaf. Stir in parsley, thyme and sage. Season to taste with salt and pepper.