In a large bowl, sift together the flour, baking soda, salt and cocoa powder.
In a separate bowl, whip together the sugar, coconut oil, vanilla and pumpkin. Add the beer and stir again until everything is homogeneous.
Using a hand- or stand- mixer, add the aquafaba and the cream of tartar to the bowl. Whip for about 6-10 minutes, or until soft peaks form.
Add the wet ingredients to the dry and stir to combine. Carefully fold the whipped aquafaba into the cake batter. Pour into a prepared bundt pan.
Bake in a preheated 350 degree oven for 40 minutes, or until a toothpick inserted in the centre comes out clean. Allow to cool, then remove from the pan.
To make the ganache, melt chocolate and milk together over a bain marie, adding more milk if needed to get the right constancy. Pour over the cake and allow to drip down the sides.