Prepare the flax eggs by mixing the ground flaxseed with water and set aside to thicken.

In a large bowl, cream the cold vegan butter, brown sugar, and granulated sugar together for about 4 minutes until light and fluffy. Scrape down the sides of the bowl as needed.

Add the vanilla extract and mix until well combined.

Add the prepared flax eggs and mix again until incorporated.

In a separate bowl, whisk together the flour, baking powder, baking soda, cornstarch, and salt.

Gradually mix the dry ingredients into the wet ingredients until just combined. Avoid overmixing.

Fold in the chocolate chips, crushed graham crackers, and pieces of marshmallow.

Weigh out the cookie dough into 3-ounce balls and refrigerate for at least 30 minutes (do not skip this step!).

Preheat the oven to 375°F (190°C) while the dough is chilling.

Bake the cookies on a parchment-lined baking sheet for 18-20 minutes, rotating the sheet halfway through for even baking.

Look for a matte finish on top; if they’re still shiny, they need more time.

Let the cookies cool for 30-45 minutes to firm up before enjoying.