@Regular_user2 one of few things may have happened:
1) Mielle (or somebody) wanted pancakes so the cook had to go along with it even if they lacked sugar.
2) Cook is stupid and just picked a dish that uses sugar even if they have no sugar.
3) Cook uses a lot of sugar to appeal as better than others.
(Explanation: addictive effects of sugar making them think it's actually good)
Cook easily could have picked a dish that doesn't require to add sugar but went along with what I guess are pancakes which, if not required by his employer, is a silly choice.
That's probably just author's way to show that the lack of sugar on the market is not imaginary but is a fact. Maybe some more time passed like when it happened with the wig, who knows. I guess it's another reason to read the novel.
Although, after I found this on the internet:
In the Renaissance, a new richness appeared and sugar became prevalent in most dishes--and counter to what we know today, because it was naturally sweet, it was considered "healthy" so the chefs of the time used it in everything. Butter and oil also became popular to thicken sauces.
Source:
https://www.crystalking.com/thefoodofrenaissanceitaly
So simply they are used to sweet things and the cook in fact used it everywhere, huh.