1. Place each chicken breast between pieces of plastic wrap. Working from center outward, lightly pound with a flat mallet or rolling pin to less than 1/4 inch thickness. Remove plastic wrap
2. In a medium bowl, toss together spinach, 1/4 cup of bread crumbs, and cheese. Divide mixture among centers of flattened breasts. Roll up to enclose filling completely, pressing edges together to adhere. Dip rolls into egg, then roll in remaining crumbs to coat lightly.
3. In a large frying pan, melt butter over medium heat. Add chicken and cook, turning carefully to brown both sides, about 8 minutes. Remove rolls from pan.
4. Add soup, milk, and marsala to pan. Bring to a boil, stirring up browned bits on bottom. Return rolls to pan. Reduce heat to medium-low, cover, and simmer until chicken is white throughout, about 10 minutes.