Heat the olive oil in a large heavy-bottomed pan over medium heat until shimmering and fragrant.
Add the finely chopped onion and sauté, stirring frequently, until translucent and soft, about 5 minutes. The onions should become fragrant and slightly golden around the edges.
Stir in the minced garlic and cook for 30 seconds until fragrant, being careful not to burn it. You’ll notice a spicy aroma and the garlic will turn slightly golden.
Add the grated carrots and chopped celery, then cook for about 5-7 minutes, stirring occasionally. The vegetables will soften and release a sweet aroma, and the mixture will start to look slightly caramelized around the edges.
Pour in the red wine or balsamic vinegar and let it simmer uncovered for 2-3 minutes until the liquid reduces by half. The sauce will shimmer and smell rich with a tangy note.
Add the rinsed lentils and tomato paste, stirring well to coat everything evenly. Cook for another 2 minutes until the paste darkens slightly and releases a concentrated aroma.
Pour in the vegetable broth, add bay leaves, thyme sprig, and smoked paprika if using. Bring everything to a gentle simmer, then reduce heat to low and cover the pan. Let it cook for 25-30 minutes, stirring occasionally, until the lentils are tender and the sauce has thickened.
Remove the bay leaves and thyme sprig. Taste the ragu and adjust seasoning with salt and pepper. If desired, mash some lentils for a creamier texture.
Let the ragu rest off the heat for 5 minutes to allow the flavors to meld. The sauce should be thick, glossy, and fragrant, with tender lentils and a smoky, savory aroma.
Serve the hearty lentil ragu hot, garnished with fresh herbs or a drizzle of olive oil. Pair it with crusty bread or over pasta for a comforting, plant-based meal.
