In a large mixing bowl, cream together the vegan butter, granulated sugar, and brown sugar using a hand mixer on medium speed for about 2 minutes until light and fluffy.

Add the flax egg and vanilla paste/extract into the creamed mixture, mixing for another 30 seconds at low speed.

Gradually incorporate the flour, baking powder, pumpkin pie spice, and salt until just combined.

Cover the dough and chill in the refrigerator for 30 minutes to 1 hour.

Whisk together the pumpkin puree, maple syrup, oat milk, cornstarch, and additional pumpkin pie spice until smooth.

Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.

Scoop about 1.5 tablespoons of dough, roll into a ball, and place on the baking sheet with 2 inches apart.

Fill each ball's indent with about 1.5 tablespoons of the pumpkin filling.

Bake in the preheated oven for 12-14 minutes until edges are crisp and filling is crinkled.

Cool on the baking sheet for 5 minutes before transferring to a wire rack.