Preheat the oven to 350°F
In a small bowl combine all the liquid ingredients: alternative milk, almond butter, vanilla extract, maple syrup, and apple sauce. Combine until the ingredients are thoroughly mixed together and form a uniform light brown color. (As shown in pictures)
In a large bowl whisk all the dry ingredients together: almond flour, baking soda, cocoa powder, coconut sugar, and salt.
Slowly pour the wet ingredients into the dry ingredients and use a spatula to mix everything together. Fold the chocolate chip and nuts into the batter.
Drizzle ~1/2 tbsp olive oil into the cast iron. Pour the brownie mixture into the cast iron and make sure it is evenly distributed.
Press marshmallows into the brownie mixture. Transfer the brownie into the oven and bake for 20-25 minutes, or until a toothpick comes out clean.
Remove from oven and allow the brownies to cool for 2-3 minutes. Slice and serve on a separate dish, or top with ice cream and enjoy it right out the skillet!