250 ml whole milk
finely grated rind of 2 oranges
1/2 cup sugar
1/2 cup vanilla sugar
1/2 teaspoon ground cardamom
1 Tablespoon orange liqueur (I make my own by stuffing a vodka bottle with lengths of fragrant orange rind...)
1 whole egg
600 ml buttermilk
combine all ingredients but the buttermilk in a medium saucepan. Use a heavy duty immersion blender to thoroughly blend everything. If you use a wimpy one, the egg won't get totally combined with the milk and you'll end up with lumpy custard. Heat over medium low heat stirring frequently, until it begins to thicken. Pour in the buttermilk and thoroughly blend again. Continue to heat for a few more minutes, blending at the end.
Pour into a metal bowl and apply cling film to the top of the mixture. Chill for at least 2 hours.