Red lentil and sweet potato soup

I really need colourful food at this time of the year - it cheers me up no end when outside it is grey, cold and spring seems a long way off. A trip to the market brought beetroots (which went into my beetroot risotto), a bundle of bright green chard that I steamed with prawns in coconut milk and spices, and sweet potatoes.

This soup is very filling and warming, a welcome splash of orange in the bowl. Makes two portions.

What you need: 
1 finely chopped large shallot
125g red lentils
1 large sweet potato
2/3 litre vegetable stock
1/2 tsp English mustard powder
1/4 tsp sumac (optional)
Salt, pepper
Harissa (optional)
A little chopped fresh parsley

What to do:
Peel the sweet potato and cut into 2cm cubes. Rinse the lentils under the cold tap in a sieve, to remove any dust. In a large pan, sauté the shallot in a splash of vegetable oil until soft and translucent. Add the lentils to the pan, stir through then pour in the stock and add the sweet potato. Add the spices - the mustard powder and sumac, if using, then a generous pinch of sea salt and a good grinding of black pepper.

Bring the pan to the boil then turn it down to a gentle simmer and let it cook for half an hour. Red lentils can absorb a lot of water so keep an eye on the liquid level and top up with boiling water from the kettle if necessary.

When the lentils are swollen and soft and the sweet potato is completely tender, take the pan off the heat and use a stick blender to blend it. Add more salt to taste and put the pan back on the hob until it starts to bubble again. Dish up and top with the parsley.

Cook's tips: 
Even allowing for the salt in the stock and the early seasoning, I find lentils need a lot of salt to stop the soup tasting bland. Check as you go and add more if you need to. While I normally shy away from adding salt if I can get away with it, this is one dish that really needs it.

You can freeze the second portion - I like to jazz it up with a generous teaspoonful of rose harissa to add a little zing to it as it reheats.