A slice of onion
Broth for cooking
Take a large pan and fry minced onion in a few olive oil. If you have, use terracotta pan, the result is better. When onion browned add lentils with salt and pepper with 5 minutes. Add broth and a few tomatoes sauce add the broth gradually dries. It will take 40/50 min.
Taste the lentils and adjust salt in cooking.