Watercress and Corn Soup

4 cups beef broth
1 teaspoon chopped fresh parsley
¼ teaspoon marjoram
2 cups frozen or fresh corn kernels
½ cup watercress, chopped finely
3 Tablespoons butter
salt and pepper

Simmer together: broth, parsley, and marjoram for 5 minutes.  Add corn and simmer for another 20 minutes. Strain through a course sieve if desired.  Stir in watercress and butter just before serving.  Season to taste with salt and pepper.