Heat oven to 475 degrees F while you wash and slice the potatoes.
Marinate the fries in the vinegar, salt and pepper (you can bake as soon as you like but letting them sit for 15-30 minutes helps the flavor sink in).
Coat a baking sheet with some oil, then put the fries in a single layer on the sheet. Pour remaining marinade over all, then drizzle with more oil. Be sure there's enough oil so the fries don't stick. Bake for 15-25 minutes (depending on thickness of fries), stirring about every 5 minutes to avoid sticking.
When fries are golden brown and tender, remove from oven. Test taste, and sprinkle with more salt and/or vinegar if desired, and serve immediately, with a side of ketchup!