Finely chop the garlic cloves and onion. Melt the butter in a large saucepan. Sauté the garlic and onions in it. Add the turmeric, garam masala, cumin and the chopped chilli pepper. Continue to steam for 30 seconds.
Now stir in the finely chopped tomatoes, lentils, lemon juice, broth and coconut milk. Bring to the boil and then simmer over low heat for 25-30 minutes until the lentils are cooked through. To finish, season again.