How do you cook pancakes in Snoopys street fair?

You don't actually cook them. If you got the quest to cook 20 pancakes, that means that you have to collect and give 20 pancakes to Snoopy. You can do that by collecting from the pancake stall and a pancake comes out of it. Click on the pancake and give it to Snoopy. Do this 20 times until the quest is completed.