Heat the milk & cream in a heavy-based saucepan over a medium heat to just below boiling point then remove from the heat. In a large bowl, whisk the egg yolks, vanilla, flour, sugar & cardamom together until pale and fluffy. Pour over the warmed milk, whisking continuously. Pour the mixture back into the pan and cook over a very low heat for 3–4 minutes stirring continuously until smooth & thick enough to coat the back of a spoon. Remove from the heat & set aside. Cover the surface of the sauce with cling film, to prevent skin forming.