Bring a medium pot of salted water to boil. Cook the potatoes until al dente–nearly cooked through, but still slightly firm. This will take about 5-10 minutes, but test with the point of a knife as you go. Drain the potatoes.

In the same pot, over medium heat, add the olive oil, garlic, and white part of the scallions. Saute until the garlic is beginning to brown, about 1 minute. Add the vinegar, stock, and salt and bring to a boil. Simmer for 1 minute. Add the potatoes back to the pot and cook for another minute or so. Off the heat, add the green part of the scallions and toss to combine. Serve immediately.