Asparagus soup

This is really simple but surprisingly tasty and well-balanced! One key was having all the ingredients finish cooking at the same time, which magically happened for us without us paying too close attention to the timing details--sorry about that. Serves 2-3.

1 bunch asparagus
1 cube not-chicken stock in 4 c water
2 T butter
2 shallots (both halves of a big one), minced
1 medium russet potato, peeled and cut in 1cm cubes
1 bunch watercress, de-stemmed
salt and pepper
croutons: thin slices of stale baguette pan-toasted in a bit of butter

Snap the woody ends off the asparagus, cut the stems into bite-sized pieces on the bias, and reserve the tips. Simmer the woody ends in the broth in a medium pot while you prepare the rest of the ingredients. In a larger pot, saute the shallot in the butter for a nice while. Remove the asparagus ends from the stock, add the stock to the shallots, and discard the boiled asparagus (or be more creative than me and find a way to use it). Add the potatoes and simmer for a few minutes until just starting to soften, add the asparagus stems and simmer for a few more minutes until barely tender, then add the asparagus tips and watercress and simmer until everything is tender but not mushy. Season and serve with croutons.