Rinse the lentils briefly in a sieve and add the remaining ingredients (except for the tomatoes, sugar and vinegar) with 1 3/4 liters of water to a 5.5 L crockpot. Cover and let simmer on low (not the warming level - then better set to medium) for about 8 hours. Then add the canned tomatoes and, if necessary, add a little water so that the lentil soup is just covered with liquid. Now season the dish to taste with a little salt, pepper, the sugar and the vinegar. Cover again and heat to high for about another hour.
Sausages and fresh farmer`s bread go well with it.
Tip:
The bacon can also be fried in a pan beforehand. I always put the vinegar on the table so that every guest can taste their own dish.