"It was quite a simple dish, but she prepared it masterfully." - missing comma.
It's a safe rule of thumb to put a comma after "but" 90% of the time.
Viewing post in Rise of the White Flower comments
No, that is not a safe rule of thumb. If there were another clause between "but" and "she prepared it masterfully", one would need a comma. (e.g. "It was quite a simple dish, but, as she'd done many times before, she prepared it masterfully.")
As it stands, however, an additional comma would be incorrect.*Confused.* I do not follow.
We have 2 facts: 1 it was a simple dish and despite that (in other words "but") 2 she prepared it exceptionally well.
I understood it as praising her cooking skills and Catherine still giving it her all in terms of skill despite the simplicity of the dish on its own. You'd get the same opposition by breaking the structure into 2 sentences and using "However, ...".
I'd get the meaning of "It trivially easy to make, especially for someone with her cooking skills.", if the quoted text had "and" instead of "but".
Then again, maybe it's the influence of my mother tongue showing here - it strictly requires a comma after every clause.
Either way, I'm genuinely at loss, so would you mind explaining in more detail?