Peel and dice the potato. Cook in boiling water for 10 minutes, or until cooked through, then drain and mash with the milk. Cook the peas in boiling water for 3 minutes, or until tender, then drain, tip into a bowl and allow to cool. Halve, peel, destone and roughly chop the avocado, then add to the bowl. Pick, finely chop and add the mint leaves (if using), mash together well, then serve. For more information on stages of complementary feeding, click here.