Preheat the oven to 180 degrees C. Lightly grease a baking dish.
Chicken: Mix the crushed garlic into the softened butter. Cut a slit into the side of each chicken breast to make a pocket then fill with the garlic butter.
Wrap each chicken breast with two slices of prosciutto to form a parcel. Place into the baking dish with the seam-side down then pour in chicken stock.
Bake the chicken in preheated oven until no longer pink; about 30 minutes. Remove the chicken from oven and cover with a sheet of foil. Allow to rest for 10 minutes.
Sauce: Bring the cooking liquid from the chicken, the orange juice and the sugar to a simmer in a saucepan over medium-high heat. Stir in cranberries and cook until they begin to pop; about 10 minutes.
Strain through a mesh sieve, pressing to expel all of the juice. Discard the solids. To serve, cut each breast into several slices, place the slices onto serving plates and drizzle with cranberry jus.