Whisk together ground flaxseed and water in a small bowl, cover and set aside for 10-15 minutes.
Preheat oven to 350° F.
Line a muffin tin with 12 baking cups.
Whisk together flax eggs, vegan butter, plant-based milk, coconut sugar, maple syrup and vanilla in a large bowl.
In a separate bowl, mix gluten-free oat flour, salt and baking soda.
Stir dry ingredients into wet ingredients using a spoon to combine.
Stir in cocoa powder.
Fold in 1 cup of chocolate chips.
Fill baking cups with batter until used up (approximately ¾ full per cup).
Use the additional 2 tbsp. chocolate chips to top each muffin.
Bake for 18-22 minutes until toothpick comes out clean.