Preheat oven to 200 degrees, fan forced and place rack into middle of oven
Lightly grease a large baking dish with butter (dish should be large enough to hold the chicken in a single row and not on top of each other)
Lay two slices of prosciutto onto your bench
Place a chicken breast on the prosciutto and roll up
Place the wrapped chicken breast into the baking dish
Continue with the other 5 breasts, laying the breasts in an alternating pattern with the thickest end against a thin end as you place them into the dish (this will help to ensure a more even bake)
Sprinkle the breasts with a little olive oil, fresh thyme (leaves only), sea salt flakes and cracked pepper
Place into oven and bake for 22 minutes (I find this perfect timing, but if your breasts are very thick and you haven't removed the tenderloin then it may take a bit longer)
Remove chicken from oven, cover with Alfoil and allow to rest for 15 minutes
Slice chicken into thick medallions, dot with sauce and serve with accompaniments of choice