Meanwhile, boil 2kg of peeled and quartered maris piper potatoes for 15 minutes or until soft, then drain. Gently heat 200ml milk and 25g butter in a small pan. Mash until smooth, then stir in the warm buttery milk and season well.
Tip most of the shallots into the mash, discarding the thyme stalks and mix in. Top with the leftover shallots and serve.