One piece of equipment that you're probably stuck with is your oven. What makes an oven "good" is its ability to accurately measure and regulate heat. Since so many reactions in cooking are about controlling the rate of chemical reactions, an oven that keeps a steady temperature and isn’t too cold or too hot can make a huge difference in your cooking and baking.
Improve your oven’s recovery time and even out the heat: keep a pizza stone in the oven. Say you’re baking cookies: oven set to 350°F / 180°C, cookies on pan, ready to go. In an empty oven, the only thing hot is the air and the oven walls, and opening the door to pop the cookies in leaves you with just hot oven walls. I find I get much better results by keeping a pizza stone on the very bottom rack in my oven, with a rack directly above it. (Don’t place the cookie sheet directly on the pizza stone!)
The pizza stone does two things. First, it acts as a thermal mass, meaning faster recovery times for the hot air lost when you open the door to put your cookies in. Second, if you have an electric oven, the pizza stone serves as a diffuser between the heating element and the bottom of your baking tray. The heating element emits a hefty kick of thermal radiation, which normally hits the bottom side of whatever pan or bakeware you put in the oven. By interposing between the heating element and the tray, the pizza stone blocks the direct thermal radiation and evens out the temperature, leading to a more uniform heat. For this reason, you should go for a thick, heavy pizza stone; they’re less likely to crack, too. I’ve turned crappy ovens that burned everything into perfectly serviceable ones capable of turning out even "picky" dishes like soufflés just by adding a pizza stone. Just remember that like any thermal mass, a pizza stone will add lag to heating up the oven, so make sure to allow extra time to preheat your oven.
Calibrate your oven using sugar. I know this sounds crazy, and yes, you should get an oven thermometer. But how do you know that the oven thermometer is right? My three thermometers—an IR thermometer, a probe thermometer, and the oven’s digital thermometer—have registered temperatures of 325°F / 163°C, 350°F / 177°C, and 380°F / 193°C, all at the same time. (They’re all designed for accurate readings in different temperature ranges.)
It’s common practice to calibrate thermometers with ice water and boiling water because the temperatures are based on physical properties. Sugar has a similar property and can be used for checking the accuracy of your oven thermometer. Sucrose (table sugar) melts at 367°F / 186°C. It turns from a powdered, granulated substance to something resembling glass. (Caramelization is different from melting; caramelization is due to the sugar molecules decomposing—literally losing their composition—and happens over a range of temperatures coincidentally near the melting point.)
Pour a spoonful of sugar into an oven-safe glass bowl or onto some foil on a cookie sheet and place in your oven, set to 350°F / 177°C. Even after an hour, it should still be powdered. It might turn slightly brown due to decomposition, but it shouldn’t melt. If it does, your oven is too hot. Next, turn your oven up to 375°F / 190°C. The sugar should completely melt within 15 minutes or so. If it doesn’t, your oven is calibrated too cold. Check to see if your oven has either an adjustment knob or a calibration offset setting; otherwise, just keep in mind the offset when setting the temperature. Note that your oven will cycle a bit above and below the target temperature: the oven will overshoot its target temperature, then turn off, cool down, turn back on, etc. It’s possible that your oven could be "correctly" calibrated but still melt the sugar when set to 350°F / 177°C due to this overshooting, but it would have to overshoot by about 15°F / 8°C.
Learn more about this topic from Cooking for Geeks.
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