I had a 3lb roast on a bed of baby potatoes (smaller than a ping-pong ball but larger than a grape) and onions at 375F for almost 3 hours. The roast came out great (cooked to 150F internally), but the potatoes are still raw in the middle. Shouldn't they have cooked by then? And what can I do in the future to prevent this?
As per comments: There was also a pizza stone in the oven. Could that have played a factor? It was preheated with the oven, as suggested in Storing Pizza Stone in Oven. The oven was preheated about an hour (my oven doesn't beep, just has a change in light color, so sometimes we forget we were preheating and wander off).