Translation:On Saturday my dad will be cooking soup.
You mean "gotował". It's not that it 'should be', it 'can be'. In Future Compound, you have two options: either you use the form that mentions the gender (Tata będzie gotował), or you use the infinitive and hide the gender (Tata będzie gotować). OK, of course with "tata" it's not really hiding the gender, but sometimes that's what you need to do, if you translate a story with a gender plot twist at the end... ;) Anyway, both those versions are perfectly fine.