It can be very frustrating when your baking is either burnt or you are in a time crunch and needed it done 5 minutes ago.  

Changing Pan Sizes 

Some days we don’t have the pan size a recipe calls for or want to make something a different shape. You can do this but keep in mind that changing pan sizes or shapes may change your baking time. If you are using a larger pan or a square pan instead of a round pan, your batter will be thinner and baking time may decrease. If you are choosing to use a smaller pan, the baking time may need to be increased.  Usually, a pan should only be filled 1/2-2/3  with raw batter, especially cake or loaf batter, to avoid spilling over.  If you do increase or decrease the pan size, check for doneness 5-10 minutes before the time indicated in the recipe. Remember, you can always add on time, but you can’t take it back.  

Opening the Oven Door 

It’s hard to be patient when you are baking, especially if you have children helping. Keep in mind that every time you open your oven door, you will be losing heat which will increase your baking time. You could also be losing steam which may dry out your baked goods. When you do open the oven door, make sure it's for the shortest time possible or your oven will have to heat up again.  

Pre-heating 

When a recipe says to pre-heat the oven, do it. Putting anything in the oven before the oven is completely heated can prolong the cooking time, and it can cause problems with the way the leavening (rising) agent reacts. Also, many ovens will go above your set temperature when they are preheating, which could cause your first batch, especially cookies, to over-brown on the bottoms.  

Overcrowding and placement:  

Most recipes assume that you will be baking one tray or item at a time, unless specified in the recipe. If you have too many pans in the oven at once, the hot air in the oven cannot move around and causes uneven baking. If you need to have more than one pan in the oven, make sure that there's at least 2 inches between each surface (pan to pan or pan to wall). If you need to use two racks in your oven, stagger the pans so that they are not directly one on top of the other.  

Temperature: 

If your baking times are significantly shorter or longer than those called for in a recipe, there may be a calibration issue with your oven’s thermostat. This is a very common problem, and almost all ovens – even those that give the impression of precision through digital temperature displays, etc. – will be at least somewhat off in their real-world versus set temperature reading. Learn more about this with our How to: Oven Calibration.