Winter Vegetable Soup with Black Barley

Name: Winter Vegetable Soup with Black Barley
Ingredients: 5 cups vegetable broth; 1/2 cup dried black-eyed peas; 1/2 cup black barley or wheat berries, rinsed; 1 lb. cabbage, shredded (about 6 cups); 2 large ribs celery, halved lengthwise and cut into 1/2-inch slices (1 cup); 2 large parsnips, peeled and cut into 1-inch chunks (1 1/2 cups); 1/2 tsp. salt; 3/4 cup reduced-fat sour cream; 2 Tbs. Dijon mustard, preferably coarse grain, plus more to taste; 3 Tbs. chopped fresh dill or 1 1/2 sp. dried; 1 1/2 Tbs. fresh lemon juice, plus more to taste; 1 cup diced, peeled carrot; 1/2 oz. (1/2 cup loosely packed) dried porcini mushrooms; 2 cups boiling water; 2 tsp. vegetable oil; 1 cup coarsely chopped onion