Make sauce: Melt butter. Add onions; cook until soft. Remove from fire; stir in flour. Gradually add the chicken broth; stir over low fire until thickened and smooth. Add garlic and season to taste.
Near dinner time, cook and drain noodles. Reheat and add mushroom mixture. Reheat chicken in sauce, then add egg yolks beaten with heavy cream. Important: First warm the egg yolk mixture with a few spoonfuls of the hot sauce. Stir carefully over low flame. Do not boil.
To serve, line serving platter with mushroom noodles. Top with chicken in garlic cream.