Leek and potato soup

It's very wintery again, and I'm on a mission to finish up all the Christmas veg - so leek and potato soup, why not?

olive oil
3 leeks
2 onions
2 cloves garlic, crushed
vegetable stock
wholegrain mustard
marmite
chilli flakes
cream for drizzling (optional obviously)

1.  Sweat down chopped and cleaned leeks and onion.
2.  Chop potatoes into smallish cubes and add them to the onions, when a little soft add crushed garlic and keep sweating down.
3.  Add about a litre of veg stock and simmer.
4.  Add a teaspoon of wholegrain mustard and a teaspoon of marmite, taste for seasoning.
5.  When potatoes are soft zizz and adjust to the right texture.
6.  Serve, drizzle with cream if you wish ... would be vegan without the cream - and is gluten free.