Set a large soup pot or Dutch oven on the stove over medium heat.

Add the olive oil to the pot and let it warm for about 30 seconds.

Add the chopped onion, celery, and carrot to the pot.

Cook the vegetables for 6 to 8 minutes, stirring often, until the onion looks soft and the carrot has started to lose its raw firmness.

Add the sliced garlic to the pot.

Cook for 30 seconds to 1 minute, stirring, until the garlic smells fragrant but has not browned.

Add the rinsed brown lentils to the pot.

Stir the lentils for about 30 seconds so they are coated with the oil and mixed through the vegetables.

Pour the vegetable broth into the pot and add the kosher salt.

Raise the heat to high and bring the broth to a boil.

Once the pot is boiling, lower the heat to medium-low so the liquid bubbles gently. Partly cover the pot with a lid.

Cook the lentils for 20 minutes, stirring once or twice, until they are starting to soften but still have a little firmness in the center.