Rinse lentils in cold water and drain well. Then place them in a large pot of water, bring to boil, and let boil for one minute.
Drain lentils and return them to the pot. Add the 8 Cups of water and cook for about 15 minutes until the lentils are very soft. Remove the pot from heat and set aside.
Put 2 Tbs. of butter in a large saucepan and saut√© the onions and garlic with the cayenne, paprika and coriander until the onions are soft but not browned.
Add the tomatoes and the tomato paste and continue to cook for 20 minutes.
Just before you are ready to serve, add to the lentils pot. Add the lemon juice and salt to taste. Bring the soup to a boil.
After the soup comes to a boil, reduce the flame and cook for about 15 minutes. Taste and adjust seasonings.
Melt the remaining 4 T. butter and mix in the mint. Dribble mint butter over individual servings.
Serve with fresh crusty bread.