Preheat the oven to 350°F/176°C. Arrange a rack in the middle or bottom third of the oven. Line a 9x5-inch loaf pan (23x13 cm) with parchment paper, letting the excess hang over the long sides to form a sling.
Stir the vinegar into the plant-based milk and set aside to curdle. This is the vegan “buttermilk.”
Pour the aquafaba into a small bowl. Using a handheld electric mixer, whip the aquafaba on medium speed for 45-60 seconds, or until uniformly foamy.
In a large mixing bowl, add the brown sugar and oil. Mix using the electric mixer or a whisk until well combined.
Add the whipped aquafaba into the oil-sugar mixture and mix until well incorporated. Add in the “buttermilk”, pumpkin puree, maple syrup, and vanilla. Mix until smooth and the ingredients are well incorporated.
In a medium bowl, combine the flour, baking soda, baking powder, salt, and all of the pumpkin spices. Whisk well to ensure the leaveners and spices are evenly distributed.
Using a silicone spatula or large wooden spoon), add the dry ingredients into the wet ingredients and gently stir until the ingredients are just barely combined, then stop mixing! The batter doesn’t need to be (and shouldn’t be) smooth. Some lumps are normal.
Pour the batter into the prepared loaf pan and smooth out the top of the batter using a spatula or spoon.
Bake in the preheated oven for 45 to 55 minutes, or until a toothpick inserted into the top sides of the cake comes out with a few moist crumbs.
Note: I like to check the cake at 45 minutes. If the toothpick reveals batter that is still a bit gooey, return the pan to the oven for 5-10 more minutes. If you’re worried about the top overbrowning, you can loosely tent the pan with aluminum foil.
Transfer the pan to a wire rack and cool for 10-15 minutes. Then, using the parchment paper handles, remove the bread from the pan and cool on the rack for at least 30 minutes before serving. When ready to serve, drizzle the Maple Tahini Icing on top (if using) and scatter with pepitas or pistachios (if using). Store leftovers in an airtight container at room temperature or in the fridge for 2-3 days.