Preheat oven to 350F. Grease the walls of the dish, if a ramekin or another small baking dish, with a small amount of vegan butter or a neutral oil, such as avocado oil. Alternatively, line it with a circular piece of parchment paper or use nonstick spray.
Mix together the dry ingredients and the wet ingredients, except the vegan marshmallows, in a small bowl, until a wet batter forms.
Pour the chocolate mixture in an even layer into 1-2 ramekins, depending on the size. They should be filled about two-thirds of the way. Bake for 25 minutes.
Add the marshmallows on top of the batter in the oven after 25 minutes. Bake for 2 minutes more.
After ~27 minutes in the oven, the brownies will be cooked and the marshmallows will be golden brown. If the marshmallows are already starting to get too brown while in the oven, remove them before the 2 minutes are up. This will depend on the type of oven being used.
Allow the brownie to cool for 15 minutes before eating. Once cool enough to eat, serve with vegan cool whip and enjoy!