Consider replacing some of the butter with nontraditional cookie ingredients, such as nonfat plain yogurt, nonfat buttermilk or even fruit juice.
When you reduce overall fat in a cookie recipe, the resulting cookies can be dry; adding a “moist” ingredient helps keep the cookies satisfying. Try 1 to 4 tablespoons of a liquid ingredient in place of up to 4 tablespoons butter. You can even experiment with replacing some of the solid fat (i.e., butter, margarine or shortening) with some heart-healthy oil and replacing a little more of the solid fat with a nonfat liquid, such as yogurt, buttermilk or juice.
Examples of cookies that add yogurt, buttermilk or fruit juice to help keep them moist:
Double Peanut Butter-Chocolate Chewies
Holiday Cranberry-Orange Pistachio Bars
Raspberry-Chocolate Thumbprint Cookies