Saltimbocca is traditionally made with veal. But I don't eat veal, and chicken is much less expensive. Proportions for this really depend on how many people you are feeding. For the filling items, add as much or as little as you want so long as you can still fold the chicken around it. The amount of sauce made in the following recipe is for 4-6 servings.
4 medium sized chicken breasts (no monsters!)*
1 tsp ground sage
1 C fresh baby spinach, stems removed
4 slices prosciutto
4 slices fresh mozzarella
oil, salt & pepper
2 Tbsp butter
1 C Marsala wine
2 C beef stock
1 C canned tomatoes, drained (about 1/2 a can)
(at least 8 toothpicks)
Place a piece of wax paper, parchment, or plastic wrap over the chicken. Using a meat mallet, pound chicken breasts until they are evenly 1/2 inch thick. Take care not to shred the chicken. (*Chicken cutlets can be used too, pound to even out the thickness. Amount of filling may vary with cutlets.) Salt and pepper both sides of chicken. On the side that will become the inside of the saltimbocca, sprinkle with sage. Lay a piece of prosciutto over each breast. On one half, place spinach and mozzarella. Fold chicken over the filling. Secure with toothpicks.
In a large skillet, melt 1 Tbsp butter over medium-high heat with a little bit of oil (maybe 1 tsp). Dredge chicken in flour and brown on each side. Remove from skillet.
Add Marsala, stock and tomatoes. Bring to boil and make sure to scrape off any bits left on the bottom of the pan from cooking the chicken. Reduce by about 1/4. Return chicken to pan. Simmer for 10 min. Turn chicken over, cover, simmer until cooked through--about 15 more minutes.
TIP: Don't have a meat mallet? Use a heavy skillet. Small cast iron skillets work great for pounding out meat. To use a skillet most effectively this way, drop it straight down and when it hits meat, push away from you. It is one fluid movement. Think about making a U with the movement (not and L). This ensures a more even thickness, and you (hopefully) wont have bits of raw meat exploding all over your chicken.