Bistro Fish Soup - slow cooker recipe

This delicious, low-fat soup is a meal unto itself!  Just add a salad and voila, dinner is ready minutes after you arrive home from work.  This recipe comes from The Healthy Slow Cooker by Judith Finlayson.  It's a treasure trove of easy, healthy slow cooker recipes.  I have adapted it for ease of use.  Don't be intimidated by the number of ingredients - it is truly no more than about 10 - 15 minutes of prep time and the rest is the slow cooker doing all the work!  Ready made (frozen) fish stock is available at Pusateri's amongst other retailers.

2 TBSP olive oil
2 large leeks, white part with a bit of green, cleaned and thinly sliced
1 onion, diced
1 bulb fennel, trimmed, cored and chopped
4 sprigs parsley
4 cloves garlic, minced
1 tsp fennel seeds (omit if you don't have on hand)
1/2 tsp each - salt and cracked black peppercorns or black pepper
1 can (28 oz) tomatoes, including juice, coarsely chopped (San Marzano tomatoes are the sweetest by far!)
6 cups fish stock (the actual recipe calls for vegetable stock but use fish stock instead - it gives it an awesome flavor boost). If you don't have fish stock, cook with vegetable stock and instead place 2 lbs fish bones and pieces in a cheesecloth and drop in as well)
2 potatoes, diced

Rouille (optional)
1/4 cup low fat mayo
1 roasted red pepper, peeled and chopped
2 cloves garlic, minced
hot pepper sauce
finely chopped parsley

In a pan, heat oil for 30 seconds (but never allow it to smoke!)  Add leeks, fennel, onion and cooks, stirring, until fennel is soft, about 6 - 10 minutes.  Add parsley, garlic, fennel seeds (if using), peppercorns and salt and cook for one more minute while stirring.  Add tomatoes with juice and fish stock and bring to boil. Transfer to slow cooker. If using vegetable stock, add cheesecloth filled with bones, and potatoes, and stir well.  Cover and cook on low for 8-10 hours or high for 4 -5 hours, until vegetables are very tender.

Rouille:  In a mini-chopper, combine mayo, red pepper, garlic and hot pepper sauce to taste.  Process until smooth.

To serve:  ladle hot soup into bowls, add a crostini on top.  Garnish with a dollop of rouille.