Lay prosciutto evenly on a large piece of plastic wrap, slightly overlapping. Place butterflied (and pounded to an even thickness) turkey on top of the prosciutto. Reserve.
In a small saute pan melt the butter over medium low heat, add apple, leek & garlic. Saute until just soft, about 3 to 5 minutes. Remove from heat and add kale, mix and reserve. When the mixture if cool, add fontina & ½ tablespoon of the mustard.
Place filling on top of the pounded turkey leaving about 1” of empty space on one side of the turkey.
Using the plastic wrap as a help/guide, tightly roll the turkey/prosciutto.*
Spray a large, oven safe, pan with oil and add the turkey with the prosciutto seam down in the pan to seal the seam. Once it has started to crisp, about 2-4 minutes, add chicken broth, sage & thyme to the pan.
Transfer to the oven and roast, 30 minutes. Raise temperature to 400°F and cook to crisp prosciutto for 10 more minutes, until the turkey has an internal temp of 160 to 165F. Let turkey rest in the pan for 7-10 minutes (important so it’s super juicy). When you take the turkey out to rest, add the remaining mustard to the sauce. If desired, the sauce can be slightly reduced at this point. Remove herbs before serving.
Notes
The apple/kale mixture should yield about 1½ cups.
Avoid pre-cooking the kale so the juices released during cooking go into the turkey!
The prosciutto wrap helps the turkey breast to stay moist, if skipping this step– make sure to use a turkey breast & keep the skin on, adding salt since we don’t use any here.