Warm Chocolate Sauce

2/3 c. packed light brown sugar 1/4 c. cocoa 1 T. cornstarch 1 can evaporated milk 1/2 c. butter Stir together sugar, cocoa and cornstarch in a small saucepan. Gradually stir in evaporated milk. Cook over medium heat, stirring constantly until mixture thickens. Add butter; situr until melted. Cool slightly.