I don't understand what was the point of making this an Isekai...
If they wanted to create a situation where the big sister feels useless while being pampered, they could have gone with something like: "The little sister is actually to be married to a prince from another country, and has to do a lot of training in order to be ready." or "After her high school entrance exams, they realised that the little sister in actually a super genius, and she and her big sister are brought to government facilities to help furthering her genius more."
This isekai setting is not only useless for the moment, they even ignore anything what could make a bit of "Isekai drama".
Like electricity and gas working, the eggs are exactly like our earth's, same for the rest of the ingredients... No problems with language, tradition or religion. Seems like in this "medieval society", women are treated the same as men too. She can even order around a knight (and a noble at that...) without anyone batting an eye.
If this is just a cooking manga with absolutely no reason to be an isekai (I'll give it 2 more chapters), then I'm dropping this.