Soak dry lentils in water - approximately 2 hours. Alternatively, use canned lentils.
Meanwhile, cut onions, celery stalks, tomatoes, peeled potatoes and carrots into large chunks.
Place onions, celery stalks, tomatoes, and carrots in a food processor with rosemary leaves. Pulse for a few seconds (add a little water if necessary to improve mixing). Add into a pot vegetable mixture, potato chunks and previously soaked lentils. Add excess water (2 inch or 4-5cm) and remaining ingredients.
Cook covered at low temperature until potatoes are soft. Remove potatoes, mash them and place back into the pot. Cook on low heat for another hour. Stir a few times while cooking.