Preheat the oven to 180°C and line a 12 cup cupcake tin with liners.
Make the cupcakes. Add vinegar to almond milk and set aside. It will split the milk, but that is ok as it helps to create a soft cupcake texture.
Using a mortar and pestle crush up the oreo biscuits until they are a fine crumb. Set aside. In a large bowl, add sugar, oil and vanilla and beat with an electric mixer.
In another bowl, sift flour, baking powder, bicarb soda and salt and mix to combine. Slowly add dry ingredients to the wet, alternating with the milk mixture, making sure it is completely mixed through before adding more. Once batter has come together and smooth, mix through crushed oreos.
Spoon into the prepared cupcake pan lined with cases filling them about ⅔ full. Bake for 20 minutes or until cakes bounce back when lightly touched. Set aside to cool completely before frosting.
Make the buttercream frosting. Crush up the oreos again using your mortar and pestle. Make sure there are no large bits and that it is a fine crumb as it will need to be piped onto the cakes and you don’t want any biscuit pieces getting stuck.
Using a hand mixer or a stand mixer with the paddle attachment fitted, beat dairy-free butter and vanilla for 1-2 minutes until creamy.
Add 3 cups of icing sugar and beat on medium until combined. As mixture thickens, add in the almond milk. If frosting is too thin, add in an extra ½-1 cup of icing sugar until it reaches the desired consistency. Add crushed Oreos and mix until combined.
Spoon mixture into a piping bag and pipe onto cakes ensuring they are completely cool as any heat left in the cakes will melt the icing. Decorate with an extra Oreo cookie.