Preheat the oven to 425°F. Line a baking sheet with parchment and set aside.
In a large bowl, whisk the flour, baking powder, baking soda, nutritional yeast, salt, and green onions.
Place a box grater in the large bowl right over the flour mixture. Quickly grate the vegan butter into the bowl. Place the bowl in the freezer for 10 minutes.
In a small bowl, whisk together ⅔ cup of the non-dairy milk, apple cider vinegar, and miso.
Take the flour mixture and grated butter out of the freezer. With your hands, quickly pinch and mix the butter into the flour until you have a coarse mixture. It should be quite firm. Once the butter is incorporated (you still want to see little grated bits). Add the non-dairy milk mixture to the flour and butter.
Quickly stir and fold the biscuit batter until it just starts to come together and is evenly hydrated. It will look quite shaggy. Flour a surface and dump the biscuit dough out.
Form the biscuit dough into a rectangle of even thickness, about an inch and a half. Cut the dough into 8 even squares. Carefully transfer the biscuits to the baking sheet. Place the baking sheet in the freezer for 10 minutes to really firm up the butter.
Once you retrieve the biscuits, whisk together the remaining non-dairy milk and maple syrup. Brush this mixture on top of the biscuits. Sprinkle extra sliced green onions, black pepper, and flaky sea salt on top if you like.
Slide the vegan biscuits into the oven and bake for 13-17 minutes, or until the vegan biscuits are puffed up and golden brown on the edges. Let the vegan biscuits cool slightly before eating.