Preheat the oven to 375°F (190°C).

Place the chicken in a large roasting dish with a lid.

Drizzle with 1 tablespoon of the olive oil and sprinkle with the salt, pepper and basil.

Cover and cook for 30 to 40 minutes or until the chicken reaches an internal temperature of at least 165°F.

Meanwhile, heat the remaining tablespoon of olive oil in a large frying pan over medium heat.

Gently sauté the leeks and mushrooms until they have begun to soften.

Pour in the stock and let it bubble up and around the leeks and mushrooms until it begins to reduce.

Stir in the mustard.

Gradually add the cream, a bit at a time, until you have a sauce that is a nice consistency.

If the sauce becomes to thick, add a bit more wine or stock and heat through.

Remove the chicken from the oven when it is cooked and serve with the sauce poured over.