Soak the raisins in the port wine at least 1 hour or, preferably, overnight. Preheat oven to 375 degrees. In a saute pan, heat 1 tablespoon of the olive oil. When hot, saute the chicken breasts on one side until golden brown. Turn the chicken over and transfer to an ovenproof dish. Bake for 10 minutes. In the meantime, in the saute pan, heat the remaining 1 tablespoon olive oil. Add the shallots and sweat them for 2 minutes. Add the mushrooms and saute them for 2 minutes. Add the vinegar and reduce until almost dry. Stir in the raisins and their soaking liquid. Cook until the liquid is reduced by half. Add the cream or evaporated milk, nutmeg, and cornstarch mixture. Cook for 2 more minutes, but do not bring to a boil. Adjust the seasoning with salt and pepper. Spoon the sauce onto serving plates, set a chicken breast on top, and garnish with fresh herbs.