Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking dish or line it with parchment paper for easy removal.
In a large mixing bowl, combine the flour, granulated sugar, cocoa powder, baking soda, baking powder, and salt. Whisk together until well mixed.
In a separate bowl, mix the almond milk and apple cider vinegar. Allow it to sit for a few minutes to create a buttermilk effect.
Add the vegetable oil, hot coffee, and vanilla extract to the milk mixture. Stir until combined.
Pour the wet ingredients into the dry ingredients and mix until just combined. Be careful not to overmix; a few lumps are okay.
Transfer the batter into the prepared baking dish, smoothing it out evenly with a spatula.
Bake in the preheated oven for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean.
Once baked, remove the cake from the oven and let it cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.
While the cake is cooling, prepare the frosting. In a mixing bowl, beat the vegan butter until creamy.
Add the cocoa powder, powdered sugar, vanilla extract, and 2 tablespoons of plant-based milk. Beat until smooth and creamy, adding more milk if necessary to achieve a spreadable consistency.
Once the cake is completely cool, spread the frosting evenly on top. Slice into squares and enjoy!