Tip for all lentil soups: for a super creamy texture, when cooked and ready to be served, blend half of it first!
Roughly chop the onion, cut the carrot and potato into cubes, and mince the garlic. Sauté for 2-3 minutes in the olive oil.
Add the turmeric, cumin, coriander, harissa and tomato paste, stir well and sauté for another 2 minutes until fragrant.
Pour in the lentils, stir until all coated, then the broth, and reduce to a simmer for about 30 minutes, with a lid (almost totally covered but leave a small space for steam to escape), stirring regularly.
When cooked, for a perfectly creamy texture but also with a bite, blend half of the soup into a purée using a hand blender, and return that purée to the pan. Combine and cook for another 5 minutes.
Season to salt and pepper, add lemon juice and sprinkle with additional chili flakes.