In a medium bowl combine the breadcrumbs, garlic, sage (3 T) and cheese.
Place each breast between two large pieces of plastic wrap and using a meat mallet or rolling pin pound each to a 20 x 25 cm rectangle that is about 1 1/2 cm thick - about the size of a letter sheet of paper.
Remove top piece of plastic and sprinkle with 1/2 teaspoon salt and 1/4 teaspoon pepper.
Lay out the prosciutto slices overlapping slightly on a cutting board to the approximate size of the turkey roll. The width of the slices should be the length of the turkey roll.
Sprinkle breadcrumb mixture over the 2 cutlets. Begin with one roll start at the longer side and roll the turkey up as tightly as possible using the plastic wrap to hold it together if needed.
Set the roll in the centre of the prosciutto perpendicular to the slices and pull the prosciutto up and around the roll. If the slices do not wrap all around the roll then lay one piece across the bottom of your roll.
Repeat process with the second turkey roll. Cover rolls and refrigerate until ready to bake.
Optional sauce can be started ahead of time or made when the turkey is resting. Heat a 10 inch frying pan over medium high heat and add butter (and any pan drippings). Cook your mushrooms and shallots until golden brown stirring occasionally. Add sage leaves and broth a bit at a time until you have the consistency of a sauce. Season with salt and pepper. Set aside until turkey is ready.
Preheat oven to 425 degrees. Transfer the turkey roll to a baking pan and roast until the meat registers 165 degrees approximately 50 minutes. Transfer the roll to a cutting board and tent with foil for at least 10 minutes before slicing and serving.
Add any pan drippings to your sauce. Slice the turkey across and serve with smashed potatoes and sauce.