1medium head garlic, outer papery skins removed and top third of head cut off and discarded
3tablespoonsolive oil
1tablespoontomato paste, heaping
9cupslow-sodium chicken broth or vegetable broth
2medium leeks, about 1 pound, green parts chopped, white parts sliced thin crosswise
10sprigs fresh parsley leaves
4sprigs fresh thyme
2bay leaves
1/2ouncedried porcini mushrooms, rinsed
For the Soup:
114.5-ounce can diced tomatoes, drained, tomato pieces chopped coarse
2small russet potatoes, about 12 ounces, peeled and cut into 1/2-inch cubes (about 1 1/2 cups)
2medium carrots, peeled and cut into 1/2-inch cubes (about 1 cup)
1/2medium celeriac, about 12 ounces, peeled and cut into 1/2-inch cubes (about 1 1/2 cups)
1small head escarole, about 12 ounces, washed, stemmed, and leaves cut into 1-inch pieces (about 4 heaping cups)
1cupfrozen baby lima beans, 6 ounces defrosted
2tablespoonsminced fresh parsley leaves
Salt and ground black pepper
Instructions
To make the stock, heat oven to 450 degrees. Place carrot, celery, onion, portobellos, and garlic head in a large bowl. Drizzle with oil and toss to coat. Add tomato paste and toss until evenly coated. Spread vegetables in even layer on a rimmed baking sheet, set garlic head cut-side up; roast until vegetables are well browned, 25 to 30 minutes.
In a large heavy-bottomed Dutch oven combine roasted vegetables, broth, leek greens, parsley, thyme, bay, and porcini; cover and bring to simmer over medium-high heat, then reduce heat to medium-low and simmer, partially covered, 30 minutes. Remove garlic head; using tongs, squeeze garlic head at root end until cloves slip out of their skins. Using fork, mash garlic to paste in small bowl and set aside. Strain stock through large fine-mesh strainer, pressing on solids to extract as much liquid as possible; discard solids in strainer.
To make the soup, rinse out and wipe Dutch oven; add tomatoes, potatoes, carrots, celeriac, reserved whites of leeks, strained broth, and garlic paste to pot and bring to simmer over medium-high heat, then reduce heat to medium-low and simmer, partially covered, until vegetables are tender when poked with a paring knife, about 25 minutes. With back of wooden spoon, mash some potatoes against side of pot to thicken soup. Stir in escarole and lima beans; cook until escarole is wilted and limas are heated through, about 5 minutes. Stir in parsley; adjust seasonings with salt and pepper.