Preheat oven to 350 degrees and line the bottom and sides of a 9-by-13-inch baking pan with foil, leaving an overhang on all sides. In a medium bowl, whisk together flour, pie spice, baking soda, and salt; set aside.
In a large bowl, cream the butter and sugar on medium-high speed until smooth with a mixer; beat in egg and vanilla until combined. Beat in pumpkin puree. Reduce speed to low, and mix in dry ingredients until just combined. Fold in chocolate chips.
Spread batter evenly in prepared pan. Bake until edges begin to pull away from sides of pan and a toothpick inserted in center comes out with just a few moist crumbs attached, 35 to 40 minutes. Cool completely in pan.
Lift cake from pan, peel off foil, and use a serrated knife to cut into 24 squares.