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Roast the pistachios in the oven to save time. Preheat the oven to 350 °F (177 °C). Spread the pistachios on a rimmed baking sheet. Roast them for 6 to 8 minutes or until they become fragrant. Let them cool.
If you are roasting over 1⁄2 cup (120 ml) pistachios, use the oven. Choosing the oven will allow you to bake a big batch of pistachios at once. Place the oven rack in the middle of the oven. Have two racks in the oven on top of each other if you are planning to make two pans of pistachios so there is enough room. It usually takes about 15-20 minutes for most ovens to preheat. Put them in an even layer on the baking sheet. Make sure none of the pistachios are covering each other, as this will ensure they roast properly.  You can line the baking sheet with parchment paper to make it easier for you to lift the pistachios off the sheet when they are done roasting. You can use two baking sheets if needed, depending on how many pistachios you are roasting. Pop them in the preheated oven and watch them as they roast. Stir them with a spoon at the halfway mark so they roast evenly. They should take no longer than 8 minutes to roast fully.  You will know they are done if they turn light brown and start to give off a nutty, fragrant smell. You can also check that they are roasted by cutting one or two pistachios in half. They should be an even pale brown color throughout. The roasted pistachios will take about 15-20 minutes to cool on the counter. Once they are no longer hot, store them in an airtight container. They should keep for 1 to 2 weeks.