Imagine a cream soup with the tanginess of the watercress and the richness of the potatoes with a light touch of cream to give it an even more savory flavor.
In a large pot, melt the butter over medium heat and add the chopped watercress. Cook for 3 minutes: add the potato cubes, bay leaf, salt, and pepper, and add chicken stock to cover the watercress and potatoes.
Bring to a boil and lower to a simmer over medium-low heat for about 20 minutes. Partially cover the pan.
Remove the bay leaf, and with a handheld mixer or in a blender and reduce a smooth, creamy puree.
Put the watercress puree back into the cooking pan, if you were using the blender, and add the heavy cream and stir well to integrate it. Lower the heat and warm up the soup, do not boil it. Taste and season accordingly.
Giangi's Kitchen provides nutritional information, but these figures should be considered estimates, as a registered dietician does not calculate them.