Peel and finely chop the onion. Add it to a pot with the olive oil and beef short ribs. Sauté briefly, then add the lentils. Pour in enough water to cover (about 10 cups/2.4 liters).

Bring to a boil and cook for 30 minutes to 1 hour. Add a pinch of salt, stir, then turn off the heat. The soup is ready to serve.

Sprinkle black pepper on top when serving.