Slice off the leek's dark green end. Then thinly slice the remaining pale green part of leek into rings and discard the root end.
Trim off the fennel stalks and the root end. Cut fennel bulb in half and discard tough outer layers. Slice the remaining fennel crosswise.
Heat olive oil in a large pot and over medium heat. Add leek, celery, carrots and 1/2 tsp of salt and and sauté for 5-7 minutes until vegetables are soft.
Add garlic and sauté for 30 more seconds.
Add in fennel, potatoes, both types of beans, rosemary
Dilute tomato paste in 1 cup of broth and add it into a pot.
Add 5 cups of broth, 1 teaspoon of salt, 1/4 tsp of pepper, bring the soup to a boil, then reduce to simmer and cook for 10 minutes.
Stir in couscous and cook soup for 10 more minutes or until couscous is soft.
Adjust the seasoning, turn off the heat and serve with the sprinkling of parsley.