Beat butter, granulated sugar, brown sugar, vanilla and salt in large bowl until creamy. Add eggs; beat well.
Stir together flour, cocoa and baking soda; gradually add to butter mixture, beating until well blended. Mix in chocolate chips and M&M's alternately. Drop by rounded teaspoons onto ungreased cookie sheet.
Bake 8 to 10 minutes or until set. Cool slightly; remove from cookie sheet to wire rack. Cool completely. About 5 dozen cookies.