Mix together the milk and apple cider vinegar in a mixing bowl. Let sit for 5 minutes.
Whisk together the flour, cocoa powder, baking soda, and salt in a large bowl until well combined.
Add the maple syrup, coconut oil, granulated sugar and vanilla extract to the milk mixture. Mix well.
Add the liquid ingredients to the dry ingredients. Mix until combined
Spray a 6-inch round cake pan with non-stick spray. Pour the batter into the pan and smooth the top.
Cover the top of the pan completely with aluminum foil. Pinch the foil around the top of the pan to create a seal and prevent moisture from creeping in while the cake bakes.
Add 1/2 cup water to the Instant pot. If you have a handled trivet: Place the handled trivet in the bottom of the instant pot with the handles up.
Place the pan directly on the handled trivet. Cover and seal the instant pot. Cook on high pressure for 35 minutes.
When the cooking time is complete, vent and release the remaining pressure. Carefully open the lid.
Lift the cake using the trivet handles. Let the cake cool in the pan for 10 minutes.
Transfer the cake to a place. Frost and enjoy!