Although many sea-level cookie recipes will give you acceptable results at high altitudes, they can usually be improved by increasing the baking temperature 15-25F. If you notice a soapy aftertaste in your cookies, lowering the amount of baking soda or baking powder by one-eighth teaspoon called for in your regular recipe may help. If your cookies are spreading too much during baking, try reducing the sugar and/or fat content by one-eighth to one-fourth the recommended amount, or increase the flour and liquid called for by one-eighth to one-fourth the recommended amount. Many cookie recipes have higher amounts of sugar and fat than necessary even at low altitudes. For more nutritious cookies with a few less calories, replace up to one-fourth of the sugar called for in the recipe with nonfat dry milk powder. Source: Altitude Adjusters by Karen Kettlewell Harrington, University of Wyoming Cooperative Extension Service (UWCES) publication B-734, 1981, with adaptations from UWCES Cent$ible Nutrition cookbook.