Preheat oven to 375 F degrees. Lightly grease cookie sheets.
Beat butter, granulated sugar and brown sugar in a large bowl until light and fluffy. Add milk, egg, and vanilla extract; beat well. Add flour, salt and baking soda. Beat until well blended. Stir in oats and M&M candy.
Drop by rounded tablespoonfuls 2 inches apart onto prepared cookie sheets. Bake 10 to 12 minutes or until edges are golden brown. Let cookies stand 2 minutes on cookie sheets. Remove cookies to wire racks; cool completely.