Melt butter over low heat. Add flour and cook, stirring over low heat 3 to 5 minutes. Let cool. In double boiler, heat milk, bay leaf, and onion til hot, not boiling. Add butter and flour mixture and cook stirring til sauce is thickened and smooth. Strain sauce.
Beat egg yolks with whipping cream til blended. Add small amount of sauce to egg mixture ,stirring constantly. Return mixture to remaining sauce in pan. Cook til well blended and smooth
Mix dry mustard to a paste with a small amount of water. Mix with cheese, salt and red pepper and add to sauce. Whip with wire whisk til smooth and creamy, about 1 to 2 minutes. Thin sauce with additional milk if sauce is too thick. Slice hard cooked eggs and arrange in large casserole or 4 individual casseroles. Cover with mustard sauce and place bacon slices on top. Bake at 350 for 5 minutes to heat through. Serve with toast triangles. makes 4 servings