Add your cold vegan butter and sugar to a large mixing bowl or stand mixer and whip until the butter is creamed (about 2-5 minutes). Once creamed, add in your flax egg, vanilla bean paste, and pumpkin puree and beat for about 30 seconds to combine.
Next, add in the all-purpose flour and salt. Mix together until a thick cookie dough forms.
Remove the cookie dough and separate into thirds. Set aside ⅔ of the pumpkin cookie dough and roll into a ball. Add the remaining ⅓ of the cookie dough back to the mixing bowl and add 1 tsp of charcoal powder. Mix until the dough is completely black.
Roll the pumpkin dough between 2 sheets of parchment paper into a rectangle about ½ inch thick in height. Then, roll out the charcoal cookie dough between 2 sheets of parchment paper into a slightly thinner, but similar-sized rectange.
Layer the charcoal dough on top of the pumpkin cookie dough and gently roll it out to press the two colors of dough together (don't add too much pressure as you just want the dough to stick together, not blend the colors).
Then, carefully roll the dough until a log forms. Press the edges down to seal. If the dough cracks at all while you roll it up, lightly press it back together and continue rolling.
Mix the orange and black sprinkles together in a dish and begin to press them into the outside of the cookie dough log until completely covered. This step is optional so feel free to skip it if you don't want to use sprinkles!
Next, lay parchment paper on top of a large baking tray and place the rolled up cookie log on top. Place the tray with the log in the freezer for at least 15-20 minutes to solidify before cutting.
After 15-20 minutes, remove the dough from the freezer and preheat the oven to 350F. Cut the dough into 10-12 even slices that are about 1 inch wide.
Lay the slices onto the baking tray covered in parchment paper, making sure to leave space between each cookie. Bake for 14-16 minutes or until firm and very lightly browned (too browned will mean you overcooked them and cooking time will vary on how thick you cut the cookie slices). Remove from the oven and let cool on the baking sheet about 5 minutes. Once cooled, serve and enjoy!