Sort lentils: Measure then spread onto a plate or cutting board. Pick out any pieces of pebbles, grains or discolored lentils.
Rinse and drain lentils in a colander, to remove any sand or grit.
Place lentils in a medium to large saucepan then add water, oil (to prevent foaming), and the optional bay leaf for flavor.
Turn heat to medium-high and bring to a boil, uncovered. Turn heat to medium-low or low, cover and keep the lid slightly ajar so it won’t boil over. Simmer 20 minutes for slightly firm lentils and 25-30 for soft ones. Drain off any excess water.
Season as desired with herbs, salt, butter, or use in a recipe calling for cooked or canned lentils.