Bake Pastry Shells According To Package Directions. Meanwhile, Place Butter In A 2-Qt. Microwave-Safe Dish. Cover And Microwave On High For 20-30 Seconds Or Until Melted. Add The Mushrooms, Onions And Pimientos. Cover And Cook On High For 2-3 Minutes Or Until Vegetables Are Crisp-Tender. Combine Flour And Milk Until Smooth; Gradually Stir Into The Vegetable Mixture. Microwave, Uncovered, On High For 2-3 Minutes Or Until Thickened, Stirring Often. Add The Cheese, Crab, Salt And Cayenne. Cook, Covered, On High For 30-60 Seconds Or Until The Cheese Is Melted. Spoon Into The Pastry Shells; Sprinkle With Parsley.