Rinse the lentils and drain well.
Put the cloves, mustard, cumin, and coriander seeds in a spice grinder or mortar and grind them until fine.
In a medium saucepan, melt the butter with the oil over medium heat. Add the ground spices, cinnamon stick, and pepper flakes and stir for about 1 minute, or until fragrant and sizzling. Stir in the tomato paste. Add the lentils and stir to coat thoroughly.
Add the stock, water, and salt. Cover, reduce heat to low, and simmer gently for 40 to 50 minutes, or until the lentils are tender. Taste and adjust the seasoning as needed.