Kitchen Tips: Testing if Potatoes are Done - as part of the expert series by GeoBeats. How can you tell when your potato is done? There are different ways to do it. I have seen it written up in recipes using skewers and knives and forks. Honestly, if I am cooking a great baked potato, all you have to do is touch it to know. A great cooked baked potato will give under gentle pressure. If you are cooking potatoes, though, in a pot of boiling water, obviously you cannot reach your hand in there. So what you do is take a very sharp paring knife and just pierce it gently to see. If you are concerned about presentation, I would suggest using a knife versus a fork, because a fork you are gonna put a lot of holes in it and change the skin. You might actually tear the skin. So a knife works great for checking all kinds of potatoes.