In a large heavy bottomed saucepan, heat the oil
Add the onion and sweat for a few minutes
Scatter in the cumin seeds and cook for a further 2 minutes, stirring occasionally
Add the garlic, celery and carrots
Sweat for a couple of minutes
Pour in the stock
Stir in the tomato purée and coriander
Next add the lentils
Stir, bring to the boil and then simmer gently for 30 minutes
Place in a blender or use a stick blender to create a smooth soup
Re heat and season with salt and black pepper to taste
Serve with crusty bread