Preheat the oven to 400 degrees F. Spray a standard muffin pan with non-stick spray or use paper liners and spray them with a little oil.
Combine the soy milk and apple cider vinegar in a glass measuring cup and set aside to curdle. This is your "buttermilk".
In a large mixing bowl, whisk together all the dry ingredients: flour, sugar, baking powder, salt and cornstarch.
Pour in the soy milk/vinegar mixture, melted vegan butter and vanilla. Stir with a large spoon to combine, but do not over mix. Some small lumps are fine.
Fold in the chocolate chips, gently. Using a small measuring cup or ice cream scoop, add batter to the liners and fill all the way to the top. Top with a sprinkle of coarse sugar, if desired.
Bake for 22-26 minutes, until lightly golden brown on top and a toothpick inserted comes out clean. Do not over bake, or they will be dry and hard. Let cool 5 minutes in the pan, then move to a cooling rack. Eat and enjoy!
Store leftover muffins in an airtight container at room temperature for about 3 days. You can also freeze them by wrapping them in plastic wrap and placing them in a large freezer bag.