Place the potatoes in a medium pot and cover with cold water. Add 1 tablespoon of kosher salt and 1 tablespoon of vinegar. Stir well. Set the heat to high and boil the potatoes until just tender (approximately 5 minutes after water has reached a boil). Drain and cool.
1½ pounds Yukon Gold potatoes, 1 tablespoon kosher salt, 1 tablespoon distilled white vinegar
While the potatoes cool, heat 1 tablespoon of oil and 1 tablespoon of butter in a large skillet set over medium heat just until the oil shimmers. Add the onion, sprinkle with salt and pepper, and cook until translucent and tender, about 3-4 minutes. Transfer to a paper towel-lined plate and remove the skillet from the heat.
3 tablespoons vegetable oil, 2 tablespoons unsalted butter, 1 sweet yellow onion, Kosher salt & freshly ground black pepper
Cut the potatoes into quarters. Place in a bowl and toss with 1 tablespoon of oil.
Set the skillet back over medium heat and add 1 tablespoon of oil and 1 tablespoon of butter. Heat the oil and butter until the oil shimmers, then add the quartered potatoes. Season the potatoes with salt and pepper, and cook in a single layer until crispy and lightly browned on the bottom, about 6 minutes.
3 tablespoons vegetable oil, 2 tablespoons unsalted butter
Add the cooked onions and thyme to the potatoes; toss and season to taste. If desired, add cilantro, parsley, or chives. Serve immediately.
1-2 teaspoons minced fresh thyme, 1 tablespoon minced fresh cilantro