Let it boil, undisturbed, for 2 minutes, then remove it from the heat, stir in the vanilla and pour it evenly over the potatoes. Give them a toss, then place them into the oven for a total time of 1 hour. After the first 20 minutes, take them out, give them a stir and cover the pan with foil for the remaining baking time. Take them out to stir again at the 40 minute mark.