In 2-quart saucepan, 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, stirring occasionally. Stir in eggs and vanilla. Stir in flour, cocoa and salt. Stir in remaining 1 cup chocolate chips. Onto cookie sheets, drop dough by tablespoonfuls about 2 inches apart.