Peel and boil the potatoes for the mash with 1 dessertspoonful of vegetable stock for flavour.
Drain the water and mash the potatoes with the butter and vegan milk, set aside.
If the lentils aren’t already cooked, cook them and add in the rest of the ingredients until the flavours combine and everything is cooked through together.
Transfer the filling into a baking or casserole dish, then pour the cooked mash on top, spread it with a spatula and bake in the oven or under the grill until crisp and golden on top.
Bake at around 190°C/375°F/gas mark 6 for 20 minutes or so, or grill until golden on top and piping hot throughout.
Tip: Add some breadcrumbs or grated vegan melting cheese on top before baking or grilling for extra crunch and tastiness.