Saving Undercooked Meat Requires More Than Just Putting It Back In The Oven
Anyone who cooks meat knows the experience of pulling a protein out of the oven or pan just to discover it's not quite done yet. If it's something like steak, it probably isn't going to hurt you (that's why you can eat it rare, after all), and we tend to drastically overestimate the dangers of undercooked pork in America. But if it's chicken? Hoo boy. You definitely want to finish that bad boy off, because undercooked chicken is a serious health risk. Even if it isn't a health problem, though, if you're not getting your meat to the desired temp, you need to cook it more.
Fortunately, it's an easy fix when this happens. You just pop it right back in the oven as is, right? If you have unlimited time, sure; that can be a method that works really well. But if you're short on time, there are other tricks at hand to quickly get undercooked meat where you need it to be. The easiest way is to cut it into smaller pieces first.
Cutting meat into smaller pieces cuts down on cooking time
Slicing meat into smaller pieces makes sense as a method for fast cooking. Smaller pieces mean more of the protein's surface area can be exposed to heat, and it'll cook faster. This is the best way to handle poultry or pork (though not steak). You're going for an internal temperature of 165 degrees Fahrenheit with poultry and 135 degrees Fahrenheit with pork, so make sure to leave the pieces in for long enough to get there.
You also want to preserve moisture in those smaller pieces, though; because they're more exposed to heat, they're also likely to dry out more quickly. For this reason, you should top the meat with stock, sauce, or water before you bake it in the oven at 400 degrees Fahrenheit. The key is to cook it quickly but not to sacrifice dinner in the process.
Fixing undercooked steak can be a bit more complicated
OK, but what do you do if you're working with steak, specifically, and parts of it are more cooked than others? You don't want to cut steak into smaller pieces; the whole point there is to preserve as much juiciness as possible, and this will dry it out much more quickly. If it's undercooked on both the inside and outside, it's an easy fix; just cook it more in a pan, getting to the desired sear before finishing in the oven.
But if you've got a hard sear on the outside but the inside is still undercooked (sometimes known as "black and blue"), it's a little trickier. You need to cook the outside as little as possible, so preheat the oven to 500 degrees Fahrenheit with a cast-iron pan already inside. Lightly oil the pan and put in the steak for two to four minutes per side, checking the temp with a meat thermometer (medium rare is about 140 degrees). This high oven heat will evenly expose the meat (and hopefully not overcook the outside).
Meat is like any other food; you just have to know how to handle it. There's no shame in not nailing the temp on the first try; just use these methods, and you'll be able to fix the issue in no time.