Cream together vegan butter, granulated sugar, and brown sugar in a mixing bowl for about 2 minutes until light and fluffy.

Add the flax egg and vanilla extract to the creamed mixture. Mix for about 30 seconds until fully incorporated.

Gradually sift in all-purpose flour, baking powder, pumpkin pie spice, and salt. Stir gently until a thick dough forms.

Cover the dough and refrigerate for 30 minutes to 1 hour.

In a separate bowl, whisk together pumpkin puree, maple syrup, oat milk, cornstarch, vanilla extract, and extra pumpkin pie spice until smooth.

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

Scoop tablespoon-sized portions of dough, roll them into balls, and create indents in each ball using your thumb.

Spoon the pumpkin filling into each indent. Bake for 12-14 minutes until edges are crisp and filling is slightly crinkled.

Let the cookies cool on a wire rack for a few minutes before enjoying.