How to Make It
Cook the asparagus in a large saucepan of salted boiling water until crisp-tender, 3 minutes. Drain and cool under cold running water; drain and pat dry.
Season the cutlets with salt and pepper and place 2 sage leaves on each cutlet. Wrap each cutlet in a slice of prosciutto, pressing to adhere. Spread the flour in a shallow dish. Dredge the chicken in flour, dusting off the excess; transfer to a baking sheet.
Set a rack over a baking sheet. Heat 2 tablespoons of the olive oil in a large skillet. Add half of the chicken and cook over moderately high heat, turning once, until golden and just cooked through, about 3 minutes. Transfer the chicken to the rack. Repeat with the remaining olive oil and chicken.
Add the vin santo and stock to the skillet and boil over moderately high heat until the liquid is reduced by half, 4 minutes. Whisk in the butter. Pour half of the sauce into a bowl. Add half of the chicken and asparagus to the skillet and cook over moderate heat until hot, 2 minutes. Season with salt; stir in half of the parsley. Transfer the chicken and asparagus to plates and pour the sauce on top. Repeat with the remaining sauce, chicken, asparagus and parsley.