Melt butter in heavy large pot or Dutch oven over medium-high heat. Add onion, celery and carrots. Sauté until vegetables begin to soften, about 8 minutes. Add pork and marjoram; stir 1 minute. Add peas, then water, and bring to boil. Reduce heat to medium-low. Partially cover pot; simmer soup until pork and vegetables are tender peas are falling apart, stirring often, about 1 hour and 10 minutes.

Transfer hocks to bowl. Puree 5 cups soup in batches in blender. Return to pot. Cut pork off bones. Dice pork; return pork to soup. Season with salt and pepper. (Can be made 1 day ahead. Refrigerate until cold, then cover. Rewarm before serving.) add your own note