Oven-browned vegetables and lots of fresh herbs give this gravy its robust flavor. Be sure to use russet or Idaho potatoes, which are high-starch varieties that have a smooth, creamy texture and begin to fall apart when boiled.
1. Preheat oven to 425°F. Quarter 1 russet potato, and place in large Dutch oven with mushrooms, carrots, celery, onions, and garlic. Toss with olive oil. Roast 30 minutes, stirring every 10 minutes, or until vegetables are deep brown on edges.
2. Transfer Dutch oven to stove top, and stir in wine, tomato paste, and 8 cups water. Add fresh herb sprigs, bay leaves, and peppercorns, and bring to a boil. Simmer, uncovered 30 minutes. Let stand 10 minutes.
3. Strain liquid (you should have 5 cups), and discard solids. Peel remaining potato, and cut into small cubes. Return broth to pot with potato, and season with salt and pepper, if desired. Simmer, uncovered, 30 minutes, or until liquid is reduced to 2 1/2 cups. Blend liquid with potato in blender or using immersion blender. Strain gravy through sieve or fine-meshed strainer. Season with salt and pepper, if desired. Reheat before serving, if necessary.