Cook pasta according to package directions; drain.

In a large saucepan melt butter. Stir in flour and salt. Blend in milk. Cook, stirring constantly, until thickened and bubbly. Add cheese; stir until melted. Combine pasta, cheese sauce and chicken. Mix well.

Pour into 3 quart casserole. Top with cornflake crumbs. Bake at 350 degrees until hot, about 30 minutes.