In a large pot, heat 2 tablespoons of olive oil over medium-high heat. Once the oil shimmers, add 1 chopped onion and 2 finely chopped celery stalks. Sauté for about 5 minutes until the onion becomes translucent and softened. Stir in 3 minced garlic cloves, cooking for an additional 1 minute until fragrant.

Next, incorporate 1.5 cups of cubed potatoes and 2 chopped carrots into the pot. Sprinkle a pinch of salt to enhance the flavors while cooking; stir the mixture for 2 minutes.

Pour in 0.5 cup of rinsed dry green or brown lentils, along with 6 cups of vegetable broth, 0.5 teaspoon of dried thyme, and 0.5 teaspoon of marjoram. Bring the mixture to a rolling boil over high heat. Once boiling, reduce the heat to low and cover, allowing it to simmer gently for 25 to 30 minutes until the lentils are tender but not mushy.

After the lentils are tender, remove the pot from the heat and let it cool slightly. Stir in 1/3 cup of shredded cheddar cheese for a creamy texture while the soup is still warm.

For a smoother finish, take out 1 cup of the soup and mix it in a separate bowl with 2 tablespoons of sour cream. Return this mixture to the pot, stirring to combine.

Taste the soup, adjusting seasoning with additional salt if needed. Before serving, garnish with fresh herbs to brighten the dish.