Preparation

• Preheat the oven to 400˚. Place the potatoes on a baking sheet and prick all over with a fork. Rub with the vegetable oil, sprinkle with 1 teaspoon salt and bake until soft in the center, about 1 hour.
• Meanwhile, cook the bacon in a medium skillet over medium heat, flipping occasionally, until browned and crispy, 5 to 7 minutes. Transfer to a paper towel–lined plate to cool, then crumble. Leave the drippings in the skillet.
• Heat the bacon drippings over medium-low heat. Add the onions and season with ½ teaspoon salt and ¼ teaspoon pepper; stir. Cover and cook, stirring once, until the onions are translucent, about 10 minutes. Uncover, increase the heat to medium and cook, stirring, until very soft and deeply golden, about 5 more minutes. Add the balsamic vinegar, thyme and garlic and cook until fragrant, about 1 minute. Add the beef broth and cook until the liquid evaporates and the onions are caramelized, about 5 minutes.
• Halve the potatoes lengthwise. Scoop out the flesh and add it to a large bowl, being careful not to tear the skins. Add the milk, sour cream, butter and remaining ½ teaspoon each salt and pepper to the bowl and mash with a potato masher to combine. Fold in the crumbled bacon, caramelized onions, 1 cup of the cheddar and 4 sliced green onions.
• Spoon the filling into the potato skins, sprinkle with the remaining ½ cup cheddar and bake until heated through, 10 to 15 minutes. Turn the oven to broil and broil until the cheese is browned and bubbling, 3 to 4 minutes. Sprinkle with the remaining 2 green onions before serving.