Fan-assisted ovens, commonly called convection or fan ovens, blow the hot air around the inside of the oven for more efficient and even heating. Ovens without fans often have hot spots, which is particularly problematic when baking cookies and biscuits because those in the back row can burn before the front row is done. You may avoid hot spots by baking in a convection oven, but you must adjust the temperature and cook time in standard recipes so you don't overcook your cookies and biscuits. Keep the fan-assisted oven manual handy until you adjust to the switch.
Adjust the oven racks to the center position, so air can circulate evenly over the top and bottom of the baking pan.
Hang an oven thermometer from a rack inside the oven to give an accurate reading of the oven temperature. Sometimes ovens do not heat to the precise temperature that you set. A thermometer can help you achieve the correct temperature for your recipe.
Preheat the oven to about 25 degrees Fahrenheit cooler than the temperature indicated in your biscuit or cookie recipe. If the recipe calls for a baking temperature of 350 degrees F, set the fan-assisted oven to 325 degrees F. Push the button to activate the oven fan, if applicable.
Place the cookie sheet in the oven and bake the cookies or biscuits with the door closed. You can turn on the oven light to monitor the progress, but avoid opening the door, because this causes the fan to shut off until the door is closed.
Reduce the baking time by 10 to 30 percent of the recommended time in the recipe; the exact time difference varies among brands of fan-assisted ovens. For example, when baking cookies or biscuits that require 10 minutes in a standard oven, bake them for seven to nine minutes. Some oven brands advise decreasing the temperature but not the cook time, while others require decreasing the bake time while keeping the temperature the same.
Check cakes and cookies after the minimum baking time. For cookies with a 10-minute baking time in a standard oven, begin checking after seven minutes and every minute up to nine minutes until they are done. Cookies and biscuits usually spread out and are thin enough that you can see when the center is risen and cooked through. When you're baking thick cookies, insert a toothpick in the center and remove them from the oven when the toothpick comes out clean.