Butterfly the chicken breasts. To do this use a sharp knife to cut down the side of the breast. Open out the breast like a book and continue to slice through horizontally but don't cut all the way through to the other side. You now have a much thinner piece of meat that will cook more quickly.
Sprinkle the chicken with the garlic powder and some salt and pepper.
Melt the butter in a large frying pan over a medium to hot heat and add the oil to stop it burning. Then add the chicken. Leave to cook for around 5 to 8 minutes.
When you can see that the chicken is cooked more than half way through, flip it over and cook on the over side for 5 to 8 minutes until cooked through. Remove from the pan and cover with foil to rest and keep warm while you make the sauce.
Add the onion to the same frying pan and cook over a medium heat for 6 minutes until soft. Add the crushed garlic for the final minute.
Pour in the wine, if using, and bubble over a high heat for 1 minute.
Add the chicken stock, pepper and cream and simmer for a couple of minutes until the sauce has slightly thickened. Taste the sauce and add salt and pepper if needed.