Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper.
In a small bowl, mix the ground flaxseed and water to create your flax egg. Set aside for a few minutes to thicken.
In a medium bowl, whisk together the flour, cream of tartar, baking soda, salt, and pumpkin pie spice. Set aside.
In a large mixing bowl, cream together the softened coconut oil and granulated sugar until light and fluffy. Add the pumpkin puree, prepared flax egg, and vanilla extract. Mix until well combined.
Gradually add the dry ingredient mixture to the wet ingredients, mixing until a soft cookie dough forms. Be cautious not to overmix.
In a small bowl, mix the granulated sugar and ground cinnamon for the coating. Roll tablespoons of dough into balls and then roll each ball in the cinnamon-sugar mixture to coat evenly.
Place the coated cookie dough balls on the prepared baking sheet, spacing them a few inches apart. Gently press each ball down with the back of a fork to create a criss-cross pattern.
Bake in the preheated oven for 10-12 minutes, or until the edges are lightly golden. The cookies will continue to firm up as they cool.
Allow the cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.
