Start by reducing the apple cider in a small saucepan on the stove. To do this, bring apple cider to a boil, then reduce to a simmer, stirring occasionally for about 15 minutes. Once reduced to about ½ cup, remove from heat and let cool.
In a large bowl, whisk together flour, sugar, baking powder, baking soda, cinnamon, salt, and nutmeg. Pour in reduced apple cider, melted vegan butter, and dairy-free milk. Stir to combine, being careful not to over mix! If the batter seems too dry, add extra dairy-free milk in one tablespoon at a time.
Pipe the batter into a generously sprayed makeshift donut pan, filling about ¾ of the way full. Bake at 350F for about 10 minutes. Flip baked donuts onto a cooling rack and let cool completely!
After the donuts have cooled, top with a dusting of powdered sugar and enjoy warm.