Preheat oven to 375 degrees. Blend sugar and butter together until smooth and creamy. Add the egg and vanilla; blend well. Sift together the flour, salt and baking powder; combine these ingredients with the creamed mixture. Add chopped white chocolate and nuts. Scoop dough out onto a cookie sheet. Bake at 375 degrees for about 5 to 10 minutes, or until golden brown on the bottom. Let cool slightly on the cookie sheet before removing or they will break.