In a medium saucepan, combine chopped Honeycrisp apple, brown sugar, vegan butter, lemon juice, and pumpkin pie spice over medium heat. Stir frequently until the mixture bubbles, about 5 minutes. Then, add the cornstarch slurry and cook for an additional 2-3 minutes until thickened. Remove from heat and let the filling cool to room temperature.

In a large mixing bowl, cream together the vegan butter and both sugars until light and fluffy, about 3-5 minutes with an electric mixer. Next, incorporate the flax egg and vanilla extract, mixing until fully combined. Gradually add in the all-purpose flour, baking powder, pumpkin pie spice, and salt until a thick cookie dough forms, ensuring everything is well-integrated.

Cover the bowl tightly with plastic wrap or a lid, and refrigerate the cookie dough for at least 30 minutes, or up to 1 hour.

While the dough chills, preheat your oven to 350°F (175°C). Line a baking tray with parchment paper for easy cookie removal and clean-up.

Once the cookie dough is chilled, take it out of the fridge and roll it into small balls, about 1.5 inches in diameter. Roll each ball in sugar to coat, then use your thumb to create a small indentation in the center of each ball to hold the cooled apple filling.

Place the assembled cookies on the prepared baking tray, leaving some space between each cookie. Bake in the preheated oven for 14-16 minutes, or until the edges are light golden brown while the centers remain soft and slightly gooey.

Once baked, allow the Vegan Apple Pie Cookies to cool on the baking tray for about 5 minutes before transferring them to a wire rack to cool completely. Enjoy your delicious treats warm or at room temperature!