Bring vegan butter and dairy-free milk to room temperature before mixing to ensure even incorporation and prevent lumpy batter that results in dense donuts.

Mix the apple cider vinegar with dairy-free milk and let it sit for 2-3 minutes before adding to create a vegan buttermilk that tenderizes the donuts and improves texture.

Fold the dry ingredients into the wet ingredients gently until just combined; overmixing develops gluten and creates tough, chewy donuts instead of light and fluffy ones.

Apply the cinnamon sugar coating while donuts are still warm from the oven by first brushing with melted vegan butter, which helps the sugar adhere and creates a delicious caramelized crust.

Use a pastry bag or small spoon to fill each donut mold to the brim; slightly overfilled donuts bake with better rise and create the signature dome top that prevents soggy centers.