Preheat oven to 350ºF.
In a medium bowl, stir together flour, baking powder, and baking soda. In a large bowl, cream together butter, granulated sugar, and brown sugar.
Beat eggs and vanilla extract into butter mixture. Gradually stir in flour mixture.
Stir in milk chocolate chips, semi-sweet chocolate chips, white chips, and nuts.
Drop by level ¼-cupfuls, about 2 inches apart, onto ungreased baking sheets. Bake for 12 to 14 minutes or until light golden brown.
Allow cookies to cool for 2 minutes on baking sheets, then transfer to wire racks to cool completely.