1.Preheat oven 200°C (180°C fan forced). Grease 12 hole (⅓ cup/80ml capacity) muffin pan.
2.Sift flour, cocoa and sugar into large bowl, stir in butter, buttermilk, egg, liqueur and rind.
3.Spoon mixture into prepared pan. Break each chocolate into 3 or 4 pieces, push chocolate into each muffin. Make sure that chocolate does not touch sides of muffin pan and that mixture almost covers the chocolate. Bake in moderately hot oven about 20 minutes.
4.To make crème anglaise. Beat egg yolks and sugar in small bowl with electric mixer until thick and pale. Pour milk into small pan, bring to the boil, whisk milk into yolk mixture. Return mixture to pan, stir over heat, without boiling, until mixture thickens and coats back of spoon.
5.Serve muffins with crème anglaise