1. Heat oven to 375°F.
2. Beat butter, sugar and sugar substitute in medium bowl until well blended. Add egg and vanilla; beat well. Stir together flour, cocoa, baking soda and salt; add alternately with milk to butter mixture, beating until well blended. Stir in small chocolate chips. Drop by teaspoonfuls onto ungreased cookie sheet.
3. Bake 7 to 9 minutes or just until set. Remove from cookie sheet to wire rack. Cool completely. Makes 36 cookies.