Add the butter to the Thermomix bowl and mix for 40 sec/speed 5 until creamy.
Add the icing sugar, cocoa powder and milk and beat for 1 min/speed 3. Scrape down the Thermomix bowl with a spatula.
Insert the butterfly whiskand whisk for 40 sec/speed 3. This step makes the buttercream light and fluffy.
Use as needed. Makes enough to ice 18-24 cupcakes or to fill and top two 20 cm sandwich cakes.
Notes
StorageChocolate buttercream icing will last in the fridge for up to 1-2 weeks. Keep it in an airtight container, then bring it to room temperature before using. For the best texture, rewhip it in the Thermomix for a few seconds with the butterfly whisk.You can freeze chocolate buttercream icing for up to 3 months. Store it in a freezer-safe container with a tight-fitting lid, ensuring it is completely airtight to maintain freshness.