Heat oven to 325. Spray cookie sheets with cooking spray.
In 2-quart scaucepan, heat butter and 1 cup of the chocolate chips over low heat, stirring occasionally, until melted. Remove from heat; stir in brown sugar. Cool slightly, stir in remaining 1 cup chocolate chips. Onto cookie sheets, drop dough by tablespoonfuls about 2 inches apart.
Bake 10 minutes or until almost set. Cool 5 minutes; remove from cookie sheets to cooling racks.