Preheat the oven to 350°F.
In a small bowl or measuring cup, whisk together the nondairy milk and vinegar and set aside.
In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking soda, baking powder, salt, and pumpkin spice.
To your dry mixture add the pumpkin purée, oil, vanilla, and milk mixture. Beat with an electric mixer.
Line two baking sheets with ~14 liners. Fill each ~2/3 of the way full with batter.
Bake for 18-20 minutes, until a toothpick comes out clean or with only crumbs. Allow to cool.
Meanwhile, make the buttercream.
Beat the butter and shortening until fluffy. Add in the powdered sugar, vanilla, and pumpkin spice and begin to beat. Gradually add in milk as necessary until you get a creamy, fluffy texture.
Put your buttercream into a piping bag with a Wilton 2D tip (or your favorite).
Pipe onto cooled cupcakes and add an extra sprinkle of pumpkin spice!
