Preheat the oven to 350°F.
Line a 12 or 24 cup mini muffin tin with liners, or use a non-stick tin.
In a large mixing bowl, stir to combine the plant milk, orange juice, butter, and apple cider vinegar.
Mix in the ground flax seed for one minute to evenly disperse. Then stir in the vanilla.
Add the sugar, and mix thoroughly.
Add the whole wheat flour, orange zest, baking powder, baking soda and salt. Stir until just combined.
Fold in the chocolate chip pieces.
Fill each muffin well with batter. Sprinkle sugar on top of each.
If using a 24 cup muffin tin, bake for about 16-20 minutes until beginning to brown and a knife inserted in the center of the muffins comes out clean.
If using a 12 cup muffin tin, bake for about 20-24 minutes until beginning to brown and a knife inserted in the center of the muffins comes out clean.