In a large mixing bowl, cream together the vegan butter, pumpkin puree, brown sugar, and granulated sugar using an electric mixer on medium speed for about 3-4 minutes until light and fluffy. Add vanilla extract.

In a separate bowl, whisk together the all-purpose flour, baking powder, pumpkin pie spice, cornstarch, and salt. Gradually add this mixture to the wet ingredients, mixing on low speed until just combined.

Cover the bowl tightly and refrigerate the dough for at least 30 minutes.

Preheat the oven to 350°F (177°C) and line a baking sheet with parchment paper.

Once chilled, scoop 2-inch balls of dough, flatten slightly, and place on the prepared baking sheet, leaving space between cookies.

Bake for 10-12 minutes until edges are golden and centers look slightly underbaked. Allow to cool on the sheet.

Prepare the frosting by mixing the vegan butter, powdered sugar, vanilla extract, cinnamon, and pumpkin pie spice until smooth and fluffy.

Frost the cooled cookies using a piping bag or knife, and optionally sprinkle with pumpkin pie spice or toasted pecans.