Place each turkey medallion between sheets of cling film and use a rolling pin to flatten them.
Discard the cling film and lay a sage leaf and a slice of prosciutto on each piece of turkey. Secure in place with cocktail sticks.
Heat the olive oil in a pan and then add 25g/1oz of the butter. Cook the medallions, prosciutto side up, then turn over and cook the other side. Remove from the pan and place on kitchen paper. Season with salt and pepper.
Remove any excess fat from the pan and add the chicken stock and white wine. Bring to the boil and then simmer until the volume of liquid is reduced by half. Strain into a clean pan and add a squeeze of lemon juice.
Add the rest of the butter, taste and check the seasoning is to your liking.
Add the parsley and serve with the turkey.