Preheat your oven to 180c and line a muffin tray with 7 paper cases.
Pour your soy milk and apple cider vinegar into a jug, then stir to combine. Set this aside for 5 minutes to allow to thicken and create your vegan buttermilk.
Add the caster sugar and olive oil into a mixing bowl and beat together using a wooden spoon. Once pale and fluffy, whisk in your pumpkin puree and buttermilk.
Sift the dry ingredients, then fold these through the wet mixture and mix well using a wooden spoon to create a smooth batter.
Use a large cookie scoop to evenly distribute the batter between your cupcake cases. Pop these into the oven for 25 minutes, then remove and allow to cool on a wire rack.
Meanwhile, use an electric hand whisk to beat the butter until pale and fluffy. The gradually add in your icing sugar and cinnamon. Transfer your buttercream into a piping bag and pipe a generous serving of frosting onto each of the cooled cakes.
To finish, dust each cake with a little cinnamon sugar and add a cinnamon stick to garnish.
