Sort & Rinse Lentils. Before you start, check through the lentils and remove any rocks, pebbles, or weird-looking lentils. Rinse in a sieve thoroughly and set aside.
Cook The Bacon. In a large pot or Dutch oven, cook the bacon pieces over medium heat 8-10 minutes, or until crisped. Don't drain the bacon fat. In a large soup pot or Dutch oven, brown bacon. Add garlic, and cook 1 minute longer. Add lentils and vegetable broth to the pot.
Cook Veggies. Add onion, carrots, and celery to the pot with the bacon and cook 5-7 minutes to soften, stirring to scrape up any browned bits from the bottom of the pan. They may not be fully cooked through, but should be softer.
Build Flavor. Add tomato paste, garlic, salt, pepper, and smoked paprika to the pan and cook another 1-2 minutes, until fragrant.
Simmer. Add lentils and broth to the pot and stir to combine. Bring to a simmer over medium heat and cook 35-45 minutes, or until lentils are tender, adding water, as needed. The exact cooking time will vary based on the type of lentils you use, so check regularly, and feel free to add a few minutes to the cook time, as needed.
Finish The Soup. Use an immersion blender to gently pulse just 4-5 times to blend part of the soup. (If you don't have an immersion blender, you can remove 1 cup or so of the soup and pulse in a blender or food processor--be careful when blending hot soup!! Stir in vinegar and fresh herbs and stir to combine, adding more water again, if needed. (I usually end up using the full 2 cups with green lentils, though I may only need 1 cup with brown lentils)
Serve & Store. Enjoy warm with sandwiches, salad, or bread. Store leftover soup in an airtight container in the fridge 3-4 days. (The flavor will be even better the next day!)Or, freeze up to 2 months!