Preheat oven to 180° degrees Celcius.
Lightly coat chicken with seasoned flour.
Heat oil and butter in a large, oven-proof, heavy based pan and cook chicken, turning it as it cooks, until golden (approx. 20 minutes). Set aside.
Add bacon, leek, garlic and mushrooms and sauté, being careful to keep the garlic bulbs intact. Remove the garlic and set aside with the chicken.
Add wine and reduce by half. Add stock and thyme and bring to the boil. Simmer for 10-15 minutes then remove from the heat.
Add crème fraiche and mustard and stir to combine. Nestle chicken and garlic back into to the pan.
Spoon the sauce over the chicken and bake for 20-30 minutes or until the chicken cooked through.
Heat oil in a small fry pan and fry sage leaves for a minute or until bright and crispy. Drain on a paper towel.
Serve with creamy mashed potatoes and garnish with crispy sage leaves.