Prepare the flax egg. Mix 1 tablespoon ground flaxseed with 3 tablespoons water. Let it sit for about 5 minutes until thickened.

Cream the butter and sugars. Add the room-temperature vegan butter, ½ cup granulated sugar, and brown sugar to a mixing bowl. Beat with an electric mixer for about 2 minutes, until light and fluffy.

Add the wet ingredients. Mix in the flax egg and vanilla for about 30 seconds.

Make the dough. Add the flour, pumpkin pie spice, baking powder, and salt. Mix until a thick dough forms. It may look crumbly at first, but continue mixing until the dough becomes soft and holds together.

Chill. Cover the dough and refrigerate for 30 minutes to 1 hour. You can also chill it for up to 24 hours.

Make the filling. While the dough chills, whisk the pumpkin puree, maple syrup, oat milk, cornstarch, vanilla, and pumpkin pie spice in a bowl until smooth.

Preheat the oven. About 10 minutes before taking out the dough, preheat the oven to 350°F and line a baking sheet with parchment paper.

Shape the cookies. Scoop the chilled dough into 10–11 equal portions. Roll each portion into a ball, then coat it in the reserved 2 tablespoons of sugar.

Create the centers. Place the dough balls on the prepared baking sheet and gently flatten them. Use your thumb to make a deep indentation in the center, then carefully widen the indentation with your fingers.

Add the filling. Spoon about 1½ tablespoons of pumpkin pie filling into the center of each cookie, keeping the filling away from the outer cookie edges.

Bake. Arrange the cookies at least 2 inches apart. Bake for 12–14 minutes, or until the edges are crisp and the pumpkin filling looks set and slightly crinkled.

Cool. Let the cookies cool on the baking sheet for 5 minutes. If necessary, gently reshape the edges with a spoon while the cookies are still warm. Transfer them to a wire rack to finish cooling.

Finish and serve. Once completely cooled, pipe a small amount of vegan whipped cream onto each cookie and sprinkle with pumpkin pie spice.