Can I re-cook potatoes stored half-roasted in the fridge? The other day I roasted some new potatoes in olive oil, with some thyme and garlic and added some lemon later. The only problem was I didn't roast them for long enough, I roasted them for 45 mins at 200C, it should probably have been an hour. I ate some of them anyway but they were quite hard. I stored them in the fridge, they've been there for about three days. 

Can I re-roast them? They look very nice with the thyme and garlic and lemon. Or should I throw them away? What's the best way to cook them if I do keep them?
Theoretically roasting them more should cook them further, however after cooling and drying in the fridge they may not come out with a very nice texture. Try microwaving a few of them before you roast them, if microwaving cooks them to they are done and you still want to eat them afterwards then roasting is a good option. If microwaving them doesn't work out roasting isn't likely to either. 

When roasting potatoes I prefer to par-boil them before roasting, it really gives a much better result! See my answer to this question for some more details.