Grandma's Collard Greens

Cook onion and bacon in a large pot over medium-high heat until onion is soft, 5 to 7 minutes. Add chicken stock, vinegar, brown sugar, and pepper flakes; cook and stir until brown sugar has completely dissolved, 2 to 3 minutes.

Add 1/2 of the collard greens, reduce heat to medium, and cook until greens are slightly wilted, about 10 minutes. Add remaining greens, toss to combine, and simmer over medium-low heat until tender, about 30 minutes. Season with salt and pepper.