Summarize this article in one sentence.
This will keep your meat warm as you're working through multiple batches of browning. It also allows you to quickly crisp the prosciutto later on. If the butcher hasn't already cut them thin for you, use a meat pounder or rolling pin to flatten the meat. It needs to be thin in order to cook quickly and crisply. To prevent messes and splatter, cover your meat in plastic wrap before flattening it. Once it's completely melted and starting to froth, move on. You do not want to cook six pieces of chicken in the same pan, so save the rest for your second batch. It shoudln't take long, especially since your meat is so thin. Flip the cutlets once so that both sides are equally cooked. This will keep the meat hot as you finish the second batch. Remember, it only needs about 2 minutes on each side to get browned. When the chicken is all done, leave the stove on -- you'll need it for the sauce. Remove the other half of chicken from the oven and place 1-3 sage leaves over the meat. Cover with prosciutto as well. While waiting for the oven to heat you can get started on your pan sauce. Once the cold wine hits the pan it will loosen any burned or browned bits. Stir them into the sauce and let everything simmer. The oven should still be heating up. Keep your eye on it -- broiling shouldn't take too long. Don't worry yet if the oven isn't quite up to temperature. The point here is to brown the prosciutto, not cook the chicken or veal, so it doesn't have to be broil temperature just yet. Once the butter is melted, simply let the sauce keep cooking until it is ready to serve. You should have about one-third of the liquid you started with when you added the wine. This is mostly up to you. Note that broiling is very, very quick, so keep your eyes peeled. Meanwhile, the sauce should still be simmering, the liquid slowly reducing. If it is almost dry, add a little more wine to the pan. Once the broiler is off, pour some sauce over the meat and serve hot. You can garnish with fresh parsley or Parmesan, if desired. Lemon wedges are also common.

Summary:
Preheat your oven to 250F/120C. Flatten your chicken or veal cutlets to roughly 1/4" (.6cm) thickness. Heat half the butter in a sauce-pan on medium heat. Cook about half the meat for two minutes on each side, until browned. Transfer the cooked chicken to a baking sheet and place in the hot oven. Add more butter and cook the remaining meat. Place the cooked meat on a baking sheet and top each piece with prosciutto and fresh sage. Turn the oven up to broil. Add one cup (240ml) of white wine to the pan you cooked the meat with and scrape up any bits on the bottom. Pour any juice from the backing sheet into the sauce, then put the chicken in the oven. Lower the heat of the sauce to a simmer and add 1 tablespoon butter. Broil your saltimbocca for 1-3 minutes, until prosciutto is crispy. Remove the meat and garnish with sauce, serving immediately.