Roast
If only the front of something gets boiled, you're going to have to roast it next. Roasting is the best way to cook something all the way through — especially when you've only managed to boil the front of it.
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What is it that you're going to roast? A centaur (せん). Hopefully you've got a pretty big oven to roast this thing in, because centaurs are not small.