It's raw, you donkey
From Rampage Knights Wiki
How to beat the challenge
The Cook can be found in the kitchen, a special room that can be found in the Dark Castle onwards. It contains a giant cook, a carcass that can be attacked to produce food, a beer keg and a large number of enemies.
Like other giants, the giant cook has a unique attack pattern. When hit 3 times, it becomes enraged, roaring once and increasing attack speed and frequency. This cannot be interrupted by attacks by the player. To counter this, one tactic is to attack it three times, then roll away until it cools down. The giant cook will also commonly jump when attacking.
Players simply need to kill the cook to complete the challenge.
Rewards
Unlocks Cook's Hat