Place the potato cubes, shallots, garlic, jalapeno, curry powder, salt, pepper and broth in a medium saucepan over medium-high heat.
Bring to a boil, then reduce the heat to medium and cook for about 20 minutes, until the potatoes can be easily pierced with a fork.
Stir in the watercress and sorrel leaves (or substitute).
Working in batches, puree the mixture in a blender with the centre cap of its lid removed and a dish towel placed over the opening (to allow steam to escape), to form a smooth soup.
Return the soup to the saucepan as you work.
Taste, and adjust the seasoning as needed.
Divide among individual bowls.
Garnish each portion with a few small sorrel leaves; serve warm.