Heat 1/4 cup of olive oil in a large pot over medium heat.
Add the onion, celery, carrot and a generous pinch of salt and cook over medium-high heat for 5 minutes, stirring often. Add the garlic and continue to cook, stirring often for an additional 5min, until the carrot and celery are softened and the onion is translucent. Don´t rush this step, it is key for allowing the veggies to sweeten and form a rich flavor base for the soup.
Add the diced tomatoes, vegetable broth, spices, lentils, and mix well. Add 1/4-1tsp of salt. The amount of salt necessary depends on the salt level in your veggie broth. Taste the broth, is should be flavorful and a little on the saltier side. It will taste less salty after cooking.
Bring to a boil, reduce to a simmer, cover, and cook until the lentils are soft but hold their shape. Depending on the lentils that you use, this should take 25-35 minutes. Check the cooking time on the packaging of your lentils and follow the time instructions.
Thicken soup: Transfer about two cups to a blender and blend until smooth. Pour back into the soup pot. If using a stick blender, place it directly in the pot and give it about 2-3 good swirls. Don´t overdo it though!
Add the kale and cook for about 3 more minutes, just until it is wilted.
Remove from heat. Add the basalmic vinegar right before serving. This step is important! It adds a depth of flavor that sets the soup apart from the rest. Season with salt and pepper to taste.
Serve while hot with with warm crusty bread! This soup will stay good in the fridge for up to 5 days and for several months in the freezer. When reheating, be sure to re-add the basalmic vinegar as the tastes fades after storage.