Melt Butter In A Large Skillet Over Medium Heat. Saute Bell Pepper, Celery And Mushrooms Until Soft, About 5 Minutes. Stir In Onion; Mix Flour And 1/2 Cup Of Milk In A Small Bowl And Stir Mixture Into Skillet. Beat Egg Yolks Into Remaining 1 1/2 Cups Milk And Pour Into Skillet. Cook, Stirring, Until Thickened. Add Chicken And Cook For 3 To 5 Minutes, Stirring Constantly. Stir In Lemon Juice, Sherry, Paprika, Salt And Pepper. Finally, Stir In Peas And Pimento Peppers. Heat Through And Serve.