Gently warm the milk. Cover the porridge oats with the milk and leave to soak for at least 15 minutes.
Add the apple to a saucepan and pour over just enough boiling water to cover. Cover with a lid, simmering for 10-15 minutes until soft. Drain.
Add the apple and soaked oats to a blender along with the prunes and cinnamon. Blend until smooth, adding whole milk/formula or breast milk if too thick.