Bring a medium pan of water to a boil. Add the lentils and cook for 15-20 minutes, until completely cooked, drain and set aside.
Put the butter and oil in a large sauté pan and place on a medium-high heat. Once the butter melts, add the garlic and cumin, and cook for a minute. Add the tomatoes, 20g of coriander and the cooked lentils. Cook, stirring, for a couple of minutes, then add the tahini, lemon juice, 70ml of water, a teaspoon of salt and a good grind of black pepper. Turn down the heat to medium and cook gently, stirring, for a few minutes more, until hot and thickened. Roughly mash the lentils with a potato masher, so that some are broken up and you get a thick, porridge consistency.
Spread out the lentils on a flat platter, run a fork through to make a wavy pattern on top, and scatter on the sliced onion, the remaining coriander and a final drizzle of olive oil. Serve warm, or hot or I also like it cold as an alternative to hummus.
