Egg, milk and flour.
300 Cooking experience and permission to use the Cook's range.
(The cook's range reduces the chance of whatever you're cooking of burning) and 1 quest point.
Talk to the Cook in Lumbridge Castle. He'll tell you that he needs some ingredients and wants you to go get them.
Getting the ingredients:
To get an egg, you can go to the Farm North East of Lumbridge, or there is a chicken farm south of Falador. You can find some eggs near the chickens.
There's a house near the chicken farm and inside there's a bucket. If you leave the farm and go East you'll be able to see some daiy cows. Use the bucket you just took, on one of the dairy cows and you'll get a bucket of milk.
Find a pot (You can probably get one from the Lumbridge general store). Then go North West to the windmill. There's a grain field just West of the windmill. Pick one grain and then go into the windmill. Go up to the top floor and use your grain on the hopper. Operate the hopper and go back down then use your pot with the flour.
When you've got all of the ingriedients, return to the cook and he'll give you your reward.