Prepare cream sauce: melt butter, stir in flour, add milk gradually, season and stir over low heat until smooth. Remove from heat and stir a little of the sauce into unbeaten egg yolks; combine with rest of sauce and cook, stirring constantly, until thickened. Arrange chicken or turkey on split muffins on cookie sheet. Spread sauce over chicken, top with grated cheese, arrange slice of tomato on each, dot with butter and sprinkle with brown sugar. This can be done ahead and refrigerated. Just before serving, broil about three or four minutes, until lightly browned. Garnish with strip of bacon and some mushrooms.