Sweet potato soup with harissa & tahini

It’s that time of year again: soup season. This is in fact the second reason to be happy about autumn, the first I posted about yesterday: pies!

Harissa is one of my favourite spice blends, originating from the North African region of Maghreb, it is full of flavour and works so well with a wide variety of vegetables. Here I have used harissa to balance the sweetness of the vegetables and the lemon tahini adds a little zing and nuttiness. I particularly like the Spice & Green harissa blend made by my friend Melanie Hadida, but you could use a good quality supermarket version or even make your own. Here’s a recipe by Mr Ottolenghi if you want to to give it a try.

Ingredients

Serves 6-8

• 1.3kg sweet potato (unpeeled)

• 4 red onions, chopped roughly 

• 3 large garlic cloves, grated

• 2 tsp harissa spice blend

• 1 vegetable stock cube (low salt Kallo)

• 1.6L water

• 1.5 tsp sea salt 

• Toasted sesame seeds - optional to serve

Lemon tahini

• 4 tbsp tahini

• Juice of half a lemon

• 75ml water

• 1/4 tsp sea salt

Method

• Preheat the oven to 180ºc.

• Put the sweet potatoes on a baking tray and roast in their skins for about 45mins-1 hour or until they’re soft right through. This will vary depending on size.

• Heat 1 tbsp rapeseed or olive oil in a large deep pan and add the onions, cook for 20 minutes on low. Peel the sweet potatoes while the onions are cooking.

• Once the onions are softened add the harissa and warm through for a few minutes to release the flavours. Then add the crumbled stock cube, water, salt and sweet potato (break up with a spoon). Bring to the boil and simmer for 10 minutes.

• Make the lemon tahini while the soup is cooking. Put the tahini and salt in a jug or jar, squeeze in the lemon, whisk with a fork before adding the water whisking again.

• Turn off the heat and use a hand blender to thoroughly blitz the soup to a smooth consistency.

• Serve with a drizzle of tahini (about 1/2 tbsp) and a good pinch of sesame seeds.

Tip

• Tahini goes very thick when you first add water, keep going it’ll loosen up. Or use a small blender to avoid this problem.

• You might need to add a little water to the tahini each time you use it as it tends to thicken up after being stored for a day in the fridge.

• Sesame seeds toast quickly and easily in a dry frying pan. Just sprinkle evenly and place on a medium heat, watching careful as they will suddenly colour. You want a pale gold brown.