Preheat your oven to 180c and line a cupcake tray with cases.
Combine your milk and cider vinegar in a jug and set aside for 5 minutes to thicken.
In a large bowl, add all of your dry ingredients and mix through. Pour in your olive oil and milk mixture, then fold these together to create a smooth batter.
Divide your cake mixture between 7 cupcake cases ( I like to use an ice cream scoop for this) and pop into the oven for 30 minutes to bake.
Whilst your cakes are cooling, whisk the butter using an electric hand mixer until pale and fluffy. Gradually add in the icing sugar whilst continuing to mix, then beat in the Biscoff spread.
Pipe the frosting onto each of the cooled cakes, sprinkle with cinnamon sugar and add a biscuit to finish!