Dredge chicken breasts in flour and shake off excess. Mix together egg and milk until thoroughly combined. Dip chicken into egg mixture, then press into chopped hazelnuts.
Heat olive oil in a skillet over medium heat. Add chicken, and cook until golden brown on both sides, and no longer pink in the center, about 5 minutes per side. Once done, place chicken on a paper towel-lined plate, and keep warm.
Increase heat to high, and pour in wine to deglaze. Stir in mushrooms, prosciutto, and spinach; cook until the mushrooms have softened, about 5 minutes. Pour in cream, bring to a simmer, then reduce heat to medium, and simmer for 5 minutes more. Ladle sauce over chicken to serve.
