When you set the oven dial — or select the digital temperature — to 350 degrees, is it actually baking at that heat? There are a couple of ways to find out.
Put your baking rack in the middle position of the oven and put a baking thermometer in the center of it. Turn the oven to 350 degrees and let it warm up for 30 minutes. Then check the thermometer to see if it reads close to 350.
The alternative used by professional chefs is an electronic baking thermostat with a probe that will digitally collect high and low temperature fluctuations. Typically a chef would take readings at the 30 and 60 minute marks and then average out the findings.
For the everyday baker with an older oven, a thermometer reading of as much as +/- 30 degrees can often be calibrated by taking the oven temperature knob off and using pliers to adjust the screw behind it, clockwise if too hot and counterclockwise if too cold. In other words, you change the way the knob sits in relation to the temperature dial. Older ovens take longer to heat up. Rather than recalibrating, perhaps simply extend baking time a little longer.
Newer model ovens have digital buttons on the control panel. Follow the directions in the owner’s manual. They usually go along the lines of pressing a command button and then an up or down arrow to change the calibration.
Gas oven temperatures fluctuate more throughout the baking process. If the baking temperature is out of line for your needs, you will have to call a professional to do any adjusting.
Also, to see whether an oven is baking evenly, pour some sugar along the bottoms of two baking sheets, bake at 400 degrees for 10 minutes, and see how evenly the sugar has browned.
It is recommended that before any big cooking event such as Thanksgiving, the oven temperature should be calibrated and tested to get the best baking results.