Can anyone explain how becoming a cook to someone is in anyway shape or form a reward?
Joining the Hero's party, even as a cook, is quite an honor. The opportunities are immense, starting from the glory of the party's achievements. And if you get fired, you are guaranteed the protagonist status.
.....
To be honest, this is kinda breaking my suspension of disbelief - more so than the battle against the demon lord.
Why?
Because Consomme has been around since the Middle Ages. It makes absolutely no sense that if they have all these various oils and soy sauces that they wouldn't have consomme as well.
Keep in mind that while consomme does take an inordinate amount of time to properly prepare, the end product itself is very simple: a very flavorful clarified soup of broth and nothing else.
The way I see it, cooking recipes are more or less an accident. They aren't connected to the ingredients available, they are mostly connected to being similar to existing recipes.
That's why so many countries in the real world have their national kitchen, even though the products they have aren't all that different.
And so, cultural exchange between different worlds is sure to bring new recipes.
Another thing that kinda broke my suspension of disbelief: the utterly lavish setting of the Duke's castle.
The only way I can see it even remotely beginning to approach this level of lavish living conditions - even taking into account that this is a fantasy setting - is if this was a massive empire where the Dukes are all the children of an Emperor. And even then, this sort of palace - throne and everything! - would have been for an Archduke; usually the Crown Prince of an Empire.
In fiction, even a humble baron's house can be this lavish. And Duke is one of the kingdom's biggest nobles.
It's the same kind of thinking that gives birth to impossibly big swords and impossibly big chests.