First, add the room-temperature vegan butter, white sugar, and brown sugar to a mixing bowl. Then, use an electric mixer to cream the butter and sugar together until fluffy (about 2 minutes).
Next, add in the flax egg and vanilla bean paste and mix together for about 20 seconds.
Add in the all-purpose flour, baking powder, baking soda, and salt. Add the flour first, then add the other ingredients on top. Then, use a fork to gently sift the baking powder, baking soda, and salt into the flour. Once sifted, mix everything together until a thick cookie dough forms.
Add the chocolate chunks and marshmallow pieces to the cookie dough and gently fold them in with a spatula until evenly distributed throughout the dough.
Cover the bowl of cookie dough with plastic wrap and add it to the fridge to chill for about 1 hour.
About 10 minutes before removing the dough from the fridge, preheat the oven to 350F and line a baking tray with parchment paper.
Remove the dough from the fridge and use a cookie scoop to scoop out 10-11 evenly sized cookies.
Place them onto the baking sheet, making sure to space the cookies at least 2 inches apart. If all of the cookies do not fit on one baking sheet, I recommend baking 5-6 cookies at a time on one tray vs. putting two trays in the oven at the same time.
Bake for 13-15 minutes until the bottoms are lightly browned and the cookies are cooked through but have slightly soft centers. The cookies will continue baking after they are removed from the oven, so the centers should still be soft, but not glossy or raw, when they are removed from the oven.
Remove the cookie tray from the oven and immediately tap the tray on the counter to produce a more “wrinkly” cookie and help deflate the cookies.
For round cookies, use a round cookie cutter (or a large mug in my case!) that is slightly larger than the cookie, and swirl the cookie inside to form it into a round cookie. This step will only work if you do it while the cookies are still warm.
Let the cookies cool on the baking sheet for 5-10 minutes, then move to a wire rack to continue cooling.
Serve the slightly cooled cookies and enjoy!