Nobody is saying he shouldn't find way to make monster meat taste good, just that he should prioritize getting her better first. There are plenty of ways to do that. For example, let her eat raw meat and get healed, but then she could say she got accustomized to his cooking and the raw food taste bad - not only that explains why she have been hidden the fact that she need monster meat, but also gives motivation for him to cook tasty food out of it.Everyone saying he should have just given her the living rabbit, isn't thinking about this in the long-term living with your monster-adjacent family member way. Like your vampire child can be perfectly healthy if you bring over a rootless drifter to be drained once a week, but the bodies and suspicions will pile up pretty quickly; instead the long-term solution is to setup a blood bank, where no one would notice a bit going missing from time to time.
Doing it this way gets him a new revenue stream, dish, and socially acceptable way for his daughter to get her needed nutrition. It even helps the adventurers with a new type of gathering quest.
I think I got it. Look at how fast the rabbit starts dissolving after it dies on page 32. Ukano would only be able to take one or two bites from each rabbit before they disappear. Since cooking the meat prevents it from decomposing, Yugudora and Sefi don't need to catch as many rabbits. If Yoishi wasn't cooking them, they'd need to catch maybe five or more times as many to yield an equivalent amount of meat. That's probably not feasible for them. It's a logistics issue rather than a culinary issue, the food tasting good is just a side effect of processing the meat.Nobody is saying he shouldn't find way to make monster meat taste good, just that he should prioritize getting her better first. There are plenty of ways to do that. For example, let her eat raw meat and get healed, but then she could say she got accustomized to his cooking and the raw food taste bad - not only that explains why she have been hidden the fact that she need monster meat, but also gives motivation for him to cook tasty food out of it.