Preheat oven to 375°. Grease cookie sheets. In a large bowl, cream together the butter, brown sugar, and white sugar until smooth. Beat in the egg and vanilla. Combine the flour and baking soda; stir into the sugar mixture. Mix in the white chocolate chips and cranberries. Drop by heaping spoonfuls onto prepared cookie sheets. Bake for 8 to 10 minutes in the preheated oven. For best results, take them out while they are still doughy. Allow cookies to cool for 1 minute on the cookie sheets before transferring to wire racks to cool completely.