4 cups chicken or vegetable broth
11/2 lbs. collard greens, stems and ribs removed
1/2 cup extra-virgin olive oil
1 large onion, coarsely chopped (about 11/2 cups)
Coarse salt and freshly ground black pepper, to taste
1 Tbs. finely chopped garlic
1/2 tsp. crushed red pepper flakes
1 Tbs. liquid smoke (available at Whole Foods)
1 (28-oz.) can whole peeled fire-roasted tomatoes, drained
In a large pot, bring the broth to a boil over medium-high heat. Add the greens and cook until tender, about 30 to 40 minutes. Drain the greens in a colander, reserving the stock.
Heat the oil in a large Dutch oven over medium heat. Add the onion and season with salt and pepper. Cook the onion, stirring frequently, until soft and translucent, five to six minutes. Add the garlic and red pepper flakes; continue to cook, stirring, for two to three more minutes. Add the liquid smoke.
Add tomatoes to the pot, breaking them up with the back of a spoon, and cook for 10 minutes. Add the cooked greens and two cups of reserved stock; simmer until heated through, about five minutes. Season with salt and pepper, and serve. Covered, the collards will keep for up to four days in the refrigerator.