Place the potatoes in a medium pot and cover with cold water. Add 1 tbsp of kosher salt and 1 tbsp of vinegar. Stir well. Set the heat to high and boil the potatoes until just tender (approximately 5 minutes after the water has reached a boil). Drain and cool.
1½ lbs. Yukon Gold potatoes, 1 tbsp kosher salt, 1 tbsp distilled white vinegar
While the potatoes cool, heat 1 tbsp of oil and 1 tbsp 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 tbsp vegetable oil, 2 tbsp 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 tbsp of oil.
Set the skillet back over medium heat and add 1 tbsp of oil and 1 tbsp 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 tbsp vegetable oil, 2 tbsp 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 tsp minced fresh thyme, 1 tbsp minced fresh cilantro