Prep: Preheat the oven to 350°F. Pour the butter and spread it over a baking sheet.: Preheat the oven to 350°F. Pour the butter and spread it over a baking sheet. : Warm, buttery aromas should be subtle as you pour, and the sheet will look lightly coated; this helps the pecans brown without sticking. I like to pour the melted butter and tilt the sheet so it forms a very thin film across the surface, which promotes even toasting. Expect a faint nutty scent as the butter warms on the metal. If your butter smokes, it is too hot, so remove it from the heat and let it cool briefly before using. A common error is using too much butter, which can cause clumping and uneven browning.
Toss: In a large bowl, mix the egg whites, sugar and cinnamon. Add the pecan halves and toss until they are fully coated.: In a large bowl, mix the egg whites, sugar and cinnamon. Add the pecan halves and toss until they are fully coated. : You will feel the tacky texture of the egg whites as the sugar and cinnamon cling to the pecan halves , and the mixture should glisten slightly. I find using a large bowl gives the nuts room to tumble so every piece gets covered. Smell the cinnamon as you stir, it should be warm but not overpowering. If the coating seems dry or patchy, gently fold the mixture again rather than adding more egg white which can make the coating dense. A typical mistake here is overmixing, which can break the nuts or create a heavy coating.
Bake: Spread the pecans onto the baking sheet evenly. Bake for 30 minutes, stirring the pecans every 10 minutes. Check after 20 minutes of baking to make sure they don't burn.: Spread the pecans onto the baking sheet evenly. Bake for 30 minutes, stirring the pecans every 10 minutes. Check after 20 minutes of baking to make sure they don't burn. : As the nuts roast, they will release a toasty, caramel fragrance and the sugar will begin to set, creating a glossy, slightly crackling surface. The visual cue to watch for is an even deepening to a golden brown color without dark spots. When you stir every 10 minutes, listen for a faint crackle as the coating firms up; this indicates progress. If the oven runs hot, rotate the sheet midway and shorten the time slightly to avoid scorching. One error I see often is skipping the periodic stirring, which can lead to uneven color and burnt edges.
Cool and serve: Cool on the baking sheet for 10-15 minutes before serving.: Cool on the baking sheet for 10-15 minutes before serving. : Cooling allows the sugar to harden into a crisp shell, and you will notice the texture change from slightly tacky to crunchy under the teeth. Leave the pecans on the sheet until they reach room temperature, then give them a gentle break apart if they stick together. The aroma at this stage is rich and sweet with a toasted backbone. If you remove them too soon they may still be soft and can clump, so patience at this point pays off. A frequent mistake is packing them away while still warm, which traps steam and softens the coating.