To sour milk, use 2 1/4 teaspoons vinegar plus enough milk to equal 3/4 cup. Heat oven to 350°. In large mixer bowl, cream butter, brown sugar, and sugar until light and fluffy. Add eggs, vanilla, and beat well. Combine flour, baking soda, baking powder and salt; add alternately with buttermilk to creamed mixture. Stir in M & M?s or chocolate chips. Drop by level 1/4 cupfuls 3? apart onto lightly greased cookie sheet. Bake 12 to 14 minutes or until lightly browned. Cool slightly, remove from cookie sheet to a wire rack. Makes about 2 1/2 dozen 4? cookies.