Preheat oven to 180C.
Line a muffin tin with cupcake liners.
Sift flour, sugar, cocoa powder and baking powder into a large bowl. Set aside.
Place grated beetroots, buttermilk, white vinegar and vanilla extract in a food processor. Blitz until processed.
Add butter and eggs. Blend until just combined.
Add beetroot mixture into the flour mixture. Whisk in gently.
Fill each cupcake liner 1/2 way full. Bake for 15-20 minutes or until a skewer inserted into the middle of the cupcakes come out clean. Transfer onto a wire rack to cool completely.
Add all ingredients for the frosting to a bowl apart from the milk and beat till smooth, if needed add some milk until a desired consistency is reached.
Spread over the cupcakes, decorate, and enjoy!