Season the chicken breasts on both sides and sprinkle lightly with cumin. Place the chicken in a shallow bowl and pour over the lemon juice. Cover and leave to marinate in the fridge for 1–2 hours.
Make up the sauce mix with 300ml boiling water, or according to the packet instructions, and set aside.
Heat the oil and butter in a frying pan. Pat dry the chicken breasts and reserve the marinade. Cook the chicken breasts over a medium heat for 5 minutes until golden brown, then reduce the heat and cook gently for a further 5 minutes on each side.
Remove the chicken from the pan, place on a heated serving dish and cover to keep warm.
Pour the reserved marinade into the frying pan and cook over a medium heat for 1–2 minutes until reduced slightly. Add the onion sauce to the pan, bring to the boil, then reduce the heat and stir in the cream. Simmer the sauce for 2–3 minutes until thickened, then spoon over the chicken breasts.
*For an extra flavour, some chopped fresh tarragon would be good added to this sauce. *For a home-made onion sauce, stir half a small sauteed chopped onion into a basic white sauce. Make up a 300ml quantity to use here.