Potluck Chicken Casserole

1/2 c chopped fresh mushrooms

3 tbsp finely chopped onion

2 cloves garlic -- minced

4 tbsp butter or margarine -- divided

3 tbsp all-purpose flour

1 1/4 c milk

3/4 c mayonnaise

4 c cubed cooked chicken

3 c cooked long grain rice

1 c chopped celery

1 c frozen peas -- thawed

1 2 oz jar diced pimientos -- drained

2 tsp lemon juice

1 tsp salt

1/2 tsp pepper

3/4 c coarsely crushed cornflakes

In a saucepan over medium heat, saute mushrooms, onion and garlic in 3 tablespoons butter until tender. Stir in flour until thoroughly combined Gradually add milk; bring to a boil. Cook and stir for 2 minutes or until thickened and bubbly. Remove from heat; stir in mayonnaise until smooth. Add chicken, rice, celery, peas, pimientos, lemon juice, salt and pepper; mixwell. Spoon into an ungreased 12x9x2=inch baking dish. Melt remaining butter; toss with cornflakes. Sprinkle over casserole. Bake, uncovered, at 350 for 30-35 minutes or until bubbly.