Begin the quest by talking to the Cook in the kitchen on the 1st floor of Lumbridge Castle. He mentions it is Duke Horacio's birthday and that he is supposed to bake a cake for it. However, he has forgotten to buy the ingredients and asks the player to bring him a bucket of milk, an egg, and a pot of flour.

A bucket spawns in the cellar of Lumbridge Castle, and a pot spawns in the kitchen. Both can be purchased from the Lumbridge General Store for 2 coins and 1 coin, respectively.

Note: You can skip the intended process by bringing a pot of flour, a bucket of milk, and an egg with you. After starting the quest with all of these items, you say that you happen to have those items with you and the cook will ask if you were planning on baking a cake, completing the quest in seconds.

Go east out of Lumbridge Castle and run north along the path until you reach the chicken coop north-west of Farmer Fred's house. Go into the coop and pick up an egg.

With an empty bucket, go north into the cow pasture. Use the empty bucket on a dairy cow to get a bucket of milk. Optional: You may talk to Gillie Groats across the river to the east in Lumbridge cow field next to the dairy cow for an explanation on how to get milk from it.

With an empty pot, leave the cow pasture and go north-west to the wheat field. Pick up a grain then enter the Mill Lane Mill to the south-west. Optional: You may talk to Millie Miller inside the mill for an explanation on how to make flour. Climb to the top floor, put the grain in the hopper, pull the lever, then climb back down to the 1st floor. Use an empty pot on the flour bin full of flour to get a pot of flour.

After collecting the ingredients, speak to to the Cook to deliver them.