In a medium-sized saucepan, heat 12 fl oz (350ml) of milk with the agave nectar, cinnamon quill and the split vanilla bean or essence. Stir in the sultanas and the barley flakes and cook over a low heat for 10 minutes, stirring until thick and the barley is soft.
Meanwhile, in a preheated, non-stick frying pan cook together the sunflower, pumpkin seeds and flaked almonds until toasted and light brown. Allow to cool, then add to the porridge.
To serve, bring the remaining milk to the boil, whisking to make as much froth as possible (I use my coffee machine steamer to do this). Spoon the porridge into serving bowls, spoon some of the hot milk froth on top and dust with the ground nutmeg.