This is the 3919th most frequent Polish word.
sernik
Cheesecake.
In this sentence, 'sernik' acts as the subject, referring to a particular cheesecake being commented on.
Ten sernik jest naprawdę pyszny!
This cheesecake is really delicious!
The usage of 'sernik' here indicates the object that was baked, a cheesecake made for a specific event.
Upiekłam sernik na urodziny.
I baked a cheesecake for a birthday.
Here, 'sernik' refers to the dish itself (cheesecake).