1. Cut 6 slices bacon into 1/4-inch-wide pieces and cook over medium heat in Dutch oven until crisp, 8 to 10 minutes. Using slotted spoon, transfer bacon to paper towel-lined plate and discard all but 2 tablespoons fat. Heat the 2 tablespoons of fat over medium heat until shimmering. Add onion and cook, stirring frequently, until softened and beginning to brown, 4 to 5 minutes. Add garlic and pepper flakes; cook until garlic is fragrant, about 1 minute. Add half of greens and stir until beginning to wilt, about 1 minute. Add remaining greens, broth, water, and 1/4 teaspoon salt; quickly cover pot and reduce heat to medium-low. Cook, stirring occasionally, until greens are tender, 25 to 35 minutes for kale and 35 to 45 minutes for collards.

2. Remove lid and increase heat to medium-high. Cook, stirring occasionally, until most of liquid has evaporated (bottom of pot will be almost dry and greens will begin to sizzle), 8 to 12 minutes. Remove pot from heat; stir in 3-4 teaspoons cider vinegar and remaining tablespoon olive oil. Season with salt, pepper, and remaining teaspoon cider vinegar. Stir reserved bacon into greens and serve.

Serves 4