Flatten turkey breast steaks between two sheets of cling film using a rolling pin. Cut each steak in half lengthways.
Lay a piece of prosciutto on each turkey steak. Top with 2 sage leaves each and secure with a toothpick.
Heat oil and half the butter in a large frying pan over high heat. Cook the turkey in two batches, prosciutto side down, 2 minutes, then turn and cook two minutes more. Transfer to a plate to keep warm.
Pour white wine into the pan to deglaze. Simmer rapidly 4-5 minutes to reduce slightly. Stir in remaining butter to melt through.
Remove and discard toothpicks from turkey. Divide between 4 plates and serve with sauce spooned over.