To unlock the Connoisseurus Rex trophy in The Sims 4, you will need to reach level 10 in the Gourmet Cooking skill.
The quickest way to reach level 10 in the Gourmet Cooking skill is to use the lot trait Homey, which will give your Sim a 50% skill gain increase. You will first need to be level 5 in the normal cooking skill, then buy the Gourmet Cooking skills books from a bookshelf.