Testing - Lettuce Soup

http://www.epicurious.com/recipes/food/views/lettuce-soup-231995
http://www.myrecipes.com/recipe/creamy-lettuce-soup

1 - I like recipes that help me use ingredients that are fragile and go off quickly. At the bottom of my refrigerator crisper drawer I often find lettuces that have turned into smelly, brown watery bags of putrification. Not yummy. And wasteful. The lettuce I had wasn't enough for a whole soup, so I got some greens out of the garden to supplement. I chose a lovely ruby frills mustard that was doing well in this West Coast winter. And I learned a lot. The mustard and lettuce was fine, but the mustard was too strong, leaving an aftertaste we couldn't quite identify as being tasty or unpleasant. We figure that there was too much mustard, and other greens, such as beet tops or chard, would help balance the flavours.
2 - The unpleasant aftertaste may have been the lettuce. This time I only used lettuce and the was a bitterness and the leaf was tough. Admittedly I used old lettuce about to flower, hoping it would be good enought to use. Softening the soup with either tender young lettuce or cutting it with young arugula and/or chard or beet tops might improve it.

1 large leek, chopped
1 garlic clove, chopped
3 tablespoons unsalted butter
3/4 teaspoon ground coriander
3/4 teaspoon salt
1/4 teaspoon black pepper
3/4 cup diced (1/3 inch) peeled potato
8 cups coarsely chopped lettuce leaves including ribs (3/4 lb) (1/3 lettuce, 1/3 mustard greens, 1/3 chard or beet tops)
1/2 cup light cream
3 cups chicken stock

1. Cook the leek and garlic in 2 tablespoons of butter, stirring, until softened. 
2. Add the coriander, salt, and pepper and cook, stirring, for about a minute. 
3. Stir in the lettuce and and the stock. Bring to a boil, then reduce to a simmer, covered, about 10 minutes.
4. Purée and transfer to a saucepan. Bring it again to a simmer, stir in the cream, then whisk in the remaining tablespoon of butter. Salt and pepper to taste.