Lay the chicken breasts on flat surface, and sprinkle them with salt and pepper. Roll up the chicken breasts and secure them with a toothpick.

Grease the bottom of a skillet with 1 tbsp of the butter, and sprinkle with the shallots. Arrange the chicken breasts, seam side down, in the skillet. Add the wine, chicken stock, and parsley. Bring to a boil, cover, and simmer for about 20 minutes, until the chicken is just cooked.

Drain and reserve all liquid from the chicken breasts; there should be about 1-1/2 cups. Remove the toothpick, cover the chicken breasts and keep them warm.

Cook the spinach leaves in a large saucepan over medium heat, in just enough water to cover for approximately 5 minutes, or until wilted. Drain well, pressing to remove excess water.

Preheat the broiler. Melt the remaining 2 tablespoons butter in a saucepan and add the flour, stirring with a wire whisk until blended, about 2 to 3 minutes. Add the reserved chicken cooking liquid, stirring until blended. When the mixture is smooth, simmer for about 5 minutes until thickened. Add the cream, and cook an additional 2 minutes. Remove the pan from the heat. Allow to cool for 5 minutes, then spoon 1/2 cup of the sauce into the egg yolk, return it to the pan, and stir briskly.

Spoon the spinach onto the center of a flameproof serving dish. Arrange the chicken breasts, seam side down, over the spinach. Spoon the sauce over the chicken and spinach and sprinkle with the cheese. Broil until bubbly and golden on top, about 5 minutes.