Testing - Chicken Breasts Stuffed with Sage Butter

This was very tasty, but there are two things about it that I'd like to improve:
1 - I think it would be better in skin-on boneless chicken breasts
2 - It was a tad too salty - what kind of prosciutto would be best and how much salt? Or, conversely, could I do without the prosciutto wrap and add some bacon fat in the sauce?

Part 1 - The sage butter
12 fresh sage leaves
3½ oz. butter, softened
4 tsps. wholegrain mustard
salt and freshly ground black pepper

1. Preheat the oven to 350F.
2. For the sage butter, chop the sage leaves finely.
3. Place the butter in a bowl, add the chopped sage leaves and mustard, and season, to taste, with salt and freshly ground black pepper. Mix together well.

Part 2 - The stuffed chicken
4 chicken breasts, skinless and boneless (Try Skin-on/Bone-in)
8 slices prosciutto (what kind?)
1 tsp. olive oil

1. For the chicken, using a sharp knife, slice into the side of each chicken breast to form a pocket.
2. Spoon a quarter of the butter mixture into each pocket and fold to enclose. (maybe tie with kitchen twine if not using the prosciutto?) If you have any of the flavoured butter left over you can roll it into a sausage shape, freeze and use (within a month) in another dish.
3. Place two prosciutto slices on a clean board so that they overlap slightly. Wrap one of the chicken breasts in the slices and roll to enclose. Repeat with the remaining prosciutto slices and chicken breasts.
4. Heat the olive oil in a heavy-bottomed frying pan. When hot, add the wrapped chicken breasts.
5. Cook over a medium heat until the prosciutto  skin? is lightly golden, about two minutes.
6. Turn the breasts over and brown the other side for another two minutes.
7. Using tongs or a fish slice, place the chicken breasts onto a baking tray and place into the preheated oven. Retain the cooking juices in the pan, as these will be used to make the sauce.
8. Cook the chicken breasts for 20 minutes, or until the chicken is completely cooked through (internal temperature of 160-165F or the chicken will feel firm to the touch and the juices will run clear when it's pierced in the thickest part).
9. When the chicken is cooked, remove from the oven and put the breasts to one side to rest for ten minutes. Keep warm.

Part 3 - The sauce
1 Tbsp. bacon fat
4½fl oz. white wine
1 garlic clove
1 fresh sage leaf
salt (be careful and measure) and freshly ground black pepper

1. While the chicken is resting, make the sauce. Heat the retained cooking juices in the pan the chicken breasts were cooked in and the bacon fat, then add the white wine. Crush the garlic clove and add to the pan. Add a sage leaf.
2. Turn up the heat and cook, scraping up the brown bits from the bottom of the pan. Cook for a couple minutes until the sauce is reduced. Season, to taste, with salt and freshly ground black pepper.

To serve, slice each breast into five slices on the diagonal, then pour the mustardy, buttery sauce over. Serve with mashed potato.