Prepare the ingredients: rinse the lentils in a fine-mesh sieve and pick out any stones or shriveled bits (this prevents grit and ensures even cooking). Dice the onion, carrot and celery to roughly the same size so they cook uniformly; mince the garlic and open the can of tomatoes.

Warm the pot: heat a heavy-bottomed Dutch oven or large saucepan over medium heat and add the olive oil and butter. The oil prevents the butter from burning while the butter adds roundness to the flavor; the combination gives a richer mouthfeel than oil alone.

Build the flavor base — sweat the vegetables: add the diced onion, carrot and celery (the classic mirepoix) and a pinch of salt. Cook over medium heat, stirring occasionally, until the onion is translucent and the edges just begin to color (about 8–10 minutes). Sweating concentrates the vegetables' natural sugars and develops depth without scorching — low-to-medium heat is key.

Add garlic and thyme and toast briefly: add the minced garlic and dried thyme and cook 30–45 seconds, stirring constantly. Toasting the garlic and dried herbs for a brief moment blooms their aromatics and prevents raw garlicky bitterness.

Deglaze and add tomatoes: add the canned diced tomatoes (with their juices) and use your spoon to scrape any browned bits off the bottom of the pan. Those browned bits are concentrated flavor (fond); deglazing loosens them and integrates them into the broth. Let the tomatoes simmer 2–3 minutes to soften their acidity.

Add lentils, broth and bay leaf: add the rinsed lentils, pour in the broth, add the bay leaf and bring the pot to a gentle boil. Then lower to a simmer and partially cover. A gentle simmer cooks the lentils evenly without breaking them apart.

Simmer until tender: cook at a gentle simmer for 25–30 minutes, stirring occasionally, until lentils are tender but not mushy. Timing varies with lentil age — test a few lentils after 20 minutes. Overcooking makes them fall apart and can thin the soup unnecessarily.

Adjust texture for body: for a restaurant-style finish, remove about 2 cups of the cooked soup to a blender (or use an immersion blender right in the pot) and purée until smooth, then stir back into the pot. This thickens the broth naturally and gives the soup a velvety, spoon-coating texture without cream.

Finish and season: add the red wine vinegar or lemon juice to brighten the flavors, then season with salt and freshly ground pepper to taste. Acidity at the end wakes up the whole pot and balances the lentils' earthiness and the tomatoes' sweetness.

Rest for flavor melding: turn off the heat and let the soup sit 5–10 minutes to allow flavors to marry. Remove and discard the bay leaf. Taste again and adjust seasoning if necessary.

Warm the rolls: while the soup rests, warm the whole-grain rolls in a 350°F (175°C) oven for 6–8 minutes to refresh and slightly crisp the crust. Warm rolls are perfect for dipping and release a toasty aroma.

Serve: ladle the soup into bowls and sprinkle with chopped fresh parsley. Serve each portion with one warm whole-grain roll on the side for dunking.