Preheat the oven to 250°F and line a baking sheet with parchment paper.: As the oven warms you will notice a gentle heat that sets the stage for slow baking, which is what creates a uniformly crisp coating rather than burnt sugar. Lining the sheet with parchment prevents sticking and makes cleanup so much easier. A common mistake is to use too high a temperature, which can brown the sugar unevenly, so resist the urge to crank the heat.
In a small bowl mix together sugar, cinnamon, and salt: Right away you will smell the warm spice of the cinnamon as it meets the sugar , and the mixture should look evenly speckled. This dry blend is what forms the final crunchy shell, so mixing thoroughly ensures consistent flavor on every nut. Avoid dumping the sugar without stirring first, since uneven distribution can create sweet or bland bites.
In a separate medium-sized bowl whisk together the egg white and vanilla until frothy.: As you whisk the egg white with the vanilla extract you will see a glossy, foamy texture form that is key to adhesion. The froth should be light and slightly airy, not stiff, which allows the dry coating to cling without clumping. Overbeating can make the egg white too stiff to properly coat the nuts, while underbeating will reduce adhesion.
Mix the pecans into the egg froth and then add the sugar mixture. Toss until evenly coated.: At this point the pecans will look glossy and tacky, and when you sprinkle the dry mix it should cling immediately. Toss gently until each half is evenly coated, watching for any large clumps of sugar that might form; break them up with a spoon. One mistake is to add all the sugar at once and not toss quickly, which can create uneven pockets of sweetness.
Evenly spread the coated pecans over the baking sheet. Bake for 1 hour until they are even brown. Be sure to stir them every 15-20 minutes.: Spread them in a single layer so each piece bakes and crisps uniformly, the visual cue being separated halves with visible sugar speckles. The even spacing allows hot air to circulate around the nuts, ensuring the coating dries and cracks rather than softening. Crowding the pan will trap moisture and create chewy spots instead of a crisp shell.
Bake for 1 hour until they are even brown. Be sure to stir them every 15 to 20 minutes: During baking the kitchen gradually fills with a toasty, spiced aroma and you will hear faint crackles as the sugar sets. Stirring every 15 to 20 minutes promotes even browning and prevents burning on the outer edges. If you skip stirring the nuts can cling together and the bottoms may darken faster than the tops, so set a timer and keep an eye on color rather than relying on clock time alone.