Cream together the butter, white sugar, and brown sugar until smooth. Beat in the egg and stir in the vanilla. Dissolve baking soda in hot water. Add to batter along with salt. Stir in flour, cream of tartar, chocolate chunks, and walnuts. Drop by large spoonfuls onto cookie sheets.
Bake for about 10 minutes in the preheated oven, or until edges are slightly browned.