In a small bowl, mix together the 1/4 cup water and 1/2 tablespoon cornstarch until a cloudy, smooth paste forms. Set the slurry aside for later use. This will help thicken your apple pie filling to the perfect texture.

Peel and dice the honeycrisp apple into small cubes. Place the diced apple in a medium saucepan along with 3 tablespoons packed brown sugar, 2 tablespoons plant-based butter, 1 tablespoon lemon juice, and 1/2 teaspoon pumpkin pie spice. Cook the mixture over medium heat, stirring occasionally, until the butter melts and the mixture begins to bubble. Pour in the cornstarch slurry from Step 1 and stir well. Continue cooking for another 5 to 10 minutes, stirring frequently, until the filling is thickened, glossy, and the apples have softened. Set the apple pie filling aside to cool completely before using it in the cookies.

In a large mixing bowl, add the 1/2 cup vegan butter (at room temperature), 1/2 cup granulated sugar, and 1/4 cup brown sugar. Using an electric mixer, cream the butter and sugars together until the mixture is fluffy, which should take about 2 minutes. Add the flax egg (made from 1 tablespoon ground flaxseed and 3 tablespoons water, already mixed) and 1 teaspoon vanilla bean paste or extract to the bowl. Mix for about 30 seconds until well incorporated. Gradually add in 1 1/2 cups all-purpose flour, 1 teaspoon pumpkin pie spice, 1/2 teaspoon baking powder, and 1/4 teaspoon salt. It's best to add the flour first, followed by the other ingredients. Mix everything together on low speed until a thick cookie dough forms. For deeper flavor, I like to make sure my vegan butter is fully softened so it creams well with the sugars.

Cover the mixing bowl with plastic wrap and place it in the refrigerator. Let the dough chill for at least 30 minutes and up to 1 hour. Chilling is important—it makes it easier to shape the dough and helps the cookies hold their shape when baking. If you'd like, you can refrigerate the dough for up to 24 hours to develop deeper flavors.

Preheat the oven to 350°F (177°C) and line a baking tray with parchment paper. Remove the chilled dough from the refrigerator. Using a cookie scoop, portion the dough into 10 evenly sized balls. Roll each dough ball between your palms to make it smooth, then roll each one in a small bowl containing 2 tablespoons of granulated sugar until coated. Place the cookie dough balls onto the lined baking sheet, spacing them at least 2 inches apart. Slightly press down on each ball with your palm to flatten. Using your thumb, create a deep indent in the center of each cookie, then use your fingers to gently widen the indent. Spoon about 1 tablespoon of the cooled apple pie filling (from Step 2) into the center of each cookie. I find that using a small spoon makes this step less messy and keeps the filling neat.

Bake the filled cookies in the preheated oven for 14 to 16 minutes, or until the edges are crisp and lightly golden, while the centers remain set but gooey. Remove the cookies from the oven and allow them to cool on the baking sheet for about 5 minutes to set further. Then, transfer them to a wire rack to cool completely before serving. Letting them cool on the baking sheet first helps prevent them from breaking apart when you lift them.