In a large pot over medium heat, cook bacon, stirring often, until fat is rendered and bacon begins to brown, 10 minutes. With a slotted spoon, transfer bacon to paper towels to drain. Add 2 tbsp. olive oil and the garlic to pot; cook, stirring often, until garlic is golden, 3 to 5 minutes.
Meanwhile, rinse greens and trim off ends. Cut out tough center ribs and slice ribs crosswise into 1-in. lengths; quarter the leaves. Add ribs to pot and cook, stirring often, until they begin to soften, 6 to 7 minutes. In batches, add leaves to pot, stirring until all are wilted. Add 1 3/4 cups chicken broth, the mustard seeds, and cooked bacon; cover and simmer until greens are tender to bite, 45 minutes to 1 hour, checking occasionally to make sure liquid hasn't completely evaporated; add more broth if it has.
Drain greens (reserve liquid for other uses) and mound in a bowl. Stir in vinegar and salt and pepper to taste, then drizzle with remaining 2 tbsp. olive oil.
Note: Nutritional analysis is per serving.