Cut the orange into small pieces and freeze them for half an hour. Place the buttermilk, blueberries and orange pieces in a blender along with the pepper and cardamom. Blend everything for a long time into a very smooth and creamy drink. Add the agave syrup and cream and give it a quick blitz. Season to taste with a bit more cardamom and pepper if desired. Pour through a sieve if desired and serve in ice-cold glasses or over ice cubes. Serve immediately. This drink makes a filling refreshment for meetings or at breakfast.