Preheat oven to 350°F (180°C) and lightly grease a 9x13" (23x13 cm) pan.
In large bowl, mix flour, baking powder, pie spice and salt.
In separate bowl, beat butter until soft and fluffy. Add granulated and brown sugar and beat until fluffy. Beat in egg. Add vanilla and pumpkin or squash puree. Mix well. The mix may look curdled which is totally fine.
Add wet ingredients to dry ingredients and stir until just combined. Stir in chocolate chips. Do not overmix. Batter will be thick.
Scrape into prepared pan and level out.
Bake for 35 to 40 minutes. Check for a golden brown all over, slightly darker at edges and a center that is firm but slightly springy to the touch. If center is still pale after 40 minutes, reduce heat by 25°F and keep baking.
Cool on wire rack in pan before slicing and serving. Extras can be frozen.