Boil a large saucepan of water and add the potatoes. Cook for 20 minutes or until the potatoes break apart when you touch them with the tip of a knife. Drain the potatoes from the water.
Add the butter, stock, salt and pepper to the now empty saucepan and heat gently until the butter has melted. Remove from the heat.
Tip the cooked potatoes back into the saucepan and mash well until the potatoes are creamy. Set aside whilst you prepare the lamb mince.
Pre-heat the oven to 200 °C/180°C fan assisted/gas mark 5.
Heat the olive oil in a wide bottomed saucepan then add the onion, carrots, celery and courgette. Cook for about 10 minutes until the vegetables have softened.
Add the lamb mince, bay and thyme leaves, stirring occasionally until the lamb has browned.
Add the sweet rice flour to the pan, mixing in well to absorb the fat. If there is any excess oil then remove it with a spoon.
Pour in the stock and stir until a thick gravy has formed.
Add the coconut aminos and mint sauce, stirring through. Cook for 5-10 minutes so all the flavours are well combined.
Remove the lamb mince from the heat then spoon into an ovenproof baking dish into an even layer.
Spoon the mashed potato over the top until it completely covers the lamb mince, then create light furrows in the potato by using the back of a fork.
Bake in the oven for 25-30 minutes until the potato is golden.