RuneScape | Cook's Assistant
In the kitchen of the castle in Lumbridge there is a cook with a quest. Ask him what is wrong and he will tell you that he has forgotten to buy some ingredients for the Duke's birthday cake: milk, and egg, and flour, and asks you to get them. This gives you the Cook's Assistant quest.
Rewards
Getting Needed Objects
Take the pot on the table, you will be using it to get the flour. Then, climb down the trapdoor in the kitchen. Here you will find a bucket to get the milk with.
Milk
Exit the castle and go east until you reach a bridge. Cross the bridge and go north until you reach the cow pen. Take the bucket and use it on a cow. It will fill up with milk.
An Egg
Exit the cow pen and get back on the road. Now, go north until you see a chicken coop to the west. Go into the chicken coop and look around for eggs. They are laid randomly so keep an eye out for them. If you don't see one, keep looking, one will appear soon. Once you have an egg, you are off to get the flour.
Flour
Exit the chicken pen. Follow the road back south until you see a bridge to the west. Cross it and follow the road to the wheat field. You can't miss it. Its a field of yellow on the map. Go into the field and pick some grain. Then, exit the wheat field and go on the north road next to it to a windmill. Go up to the top floor and put the grain in the hopper. There are some levers, right click on them and choose "operate hopper controls". Go back down to the ground floor and right click on the flour bin and empty it. This should fill your pot with flour.
Give them all to the cook
Go back to the castle kitchen and talk to the cook. This finishes the quest.