In a medium bowl, combine butter with brown & white sugar. Add egg, pumpkin, flour, spices & salt; mixing until a thick dough forms. Preheat oven to 300 F. Line a baking sheet with parchment paper. Scoop balls (about 2 tsp size), 1-inch apart from each other. Using your thumb or a sewing thimble, make a divot in the center of each ball. Bake for 25 minutes or until slightly brown. Remove cookies from oven; while hot, deepen any of the divots if needed. Place on cooling rack.