First, prepare the collard greens. Wash the leaves thoroughly under cold running water to remove any grit. Trim the thick, tough stems away from the center of each leaf and discard them. Stack a few leaves at a time, roll them into a cigar shape, and slice them into 1-inch ribbons. Set aside.
Place a large Dutch oven or heavy-bottomed pot over medium heat. Add the chopped bacon and cook, stirring occasionally, until it becomes crisp, about 8-10 minutes.
Add the chopped onion to the pot with the bacon and its rendered fat. Cook, stirring frequently, until the onion softens and turns translucent, about 5 minutes. Stir in the minced garlic and cook for another minute until fragrant.
Add the prepared collard greens to the pot in handfuls. It may seem like a lot, but they will cook down. Stir continuously until the greens are wilted, about 5-7 minutes.
Pour in the chicken broth and add the chopped sun-dried tomatoes, salt, black pepper, and optional red pepper flakes. Stir everything together well.
Bring the liquid to a gentle boil. Once it's bubbling, reduce the heat to low, cover the pot, and let it simmer.
Cook for 45 to 60 minutes, or until the collard greens are very tender. Stir occasionally. Taste and adjust seasoning with more salt if needed before serving.