First of all, preheat your oven to 180c fan.
Take a cupcake tray and place paper cases on it.
Take a mixing bowl and combine the oat milk and apple cider vinegar and mix them together. Set this mixture aside for 5 minutes to thicken and create your vegan buttermilk.
Take another mixing bowl, use a wooden spoon to mix the sugar and oil. Stir in the buttermilk mixture, then shift your dry ingredients into the bowl also
Fold everything together to create a smooth cake batter
When youyour batter is ready, divide them evenly between your cupcake cases.
Place them into your preheated oven to bake for 25 to 28 minutes.
After they baked properly remove them and allow to cool thoroughly on a wire cooling rack.
Meanwhile, for the buttercream frosting, allow your vegan butter to come to room temperature, then use a stand mixer or electric hand whisk to beat this until pale and fluffy.
Gradually add in your icing sugar whilst whisking and continue to do so until everything is fully combined.
Now, add your Biscoff spread and beat this into the frosting.
Once your cakes have fully cooled, top each of them with a swirl of buttercream.