1Heat oven to 350°F. In large bowl, stir 3/4 cup of the butter and the sugar until well mixed. Stir in flour (if dough is crumbly, mix in up to 2 additional tablespoons softened butter). Stir in remaining Cookie ingredients.
2On work surface lightly sprinkled with flour, roll dough 1/4 inch thick. Cut with 2-inch round cutter. On ungreased cookie sheets, place 1/2 inch apart.
3Bake 15 to 18 minutes or until set. Immediately remove from cookie sheets to cooling racks.
4In small microwavable bowl, microwave 1 cup chocolate chips and the oil uncovered on High 1 minute 30 seconds, stirring every 30 seconds or until mixture can be stirred smooth. Dip half of each cookie into chocolate; wipe excess on edge of bowl. Sprinkle edge of dipped half with finely chopped pistachio nuts. Place on waxed paper to set, about 1 hour.