Potluck Chicken Casserole

1/2 cup chopped fresh mushrooms
3 tablespoons finely chopped onion
2 garlic cloves, minced
4 tablespoons butter, divided
3 tablespoons all-purpose flour
1-1/4 cups milk
3/4 cup mayonnaise
4 cups cubed cooked chicken
3 cups cooked long grain rice
1 cup chopped celery
1 cup frozen peas, thawed
1 jar (2 ounces) diced pimientos, drained
2 teaspoons lemon juice
1 teaspoon salt
1/2 teaspoon pepper
3/4 cup 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 the heat; stir in mayonnaise until smooth.

Add chicken, rice, celery, peas, pimientos, lemon juice, salt and pepper; mix well. Spoon into an ungreased 13-in. x 9-in. x 2-in. baking dish.

Melt remaining butter; toss with cornflakes. Sprinkle over casserole. Bake, uncovered, at 350° for 30-35 minutes or until bubbly. Makes 8-10 servings.