Preheat the oven to 250°F (120°C). Spread the pecans on a baking sheet and roast for 8–10 minutes, or until lightly browned and fragrant. Allow to cool, then place the pecans in a plastic bag and crush them gently using a rolling pin or wooden spoon. Set aside.

In a clean, grease-free mixing bowl, add the egg whites and a pinch of salt. Using an electric mixer set to medium speed, beat until soft peaks begin to form. The mixture should appear slightly glossy with small, uniform bubbles.

Increase the speed to medium-high. Slowly add the sugar, two tablespoons at a time, while continuing to beat. This gradual addition allows the sugar to dissolve fully, giving the meringue a smooth, glossy texture.

Add the vinegar to the mixture, then increase the mixer speed to high. Beat until stiff peaks form and the meringue is thick, glossy, and holds its shape when the whisk is lifted.

Using a rubber spatula, gently fold the crushed pecans into the meringue. Take care not to overmix, as this will deflate the whipped egg whites.

Line baking sheets with parchment paper or silicone mats. Drop teaspoonfuls of the meringue mixture onto the sheets, spacing them about 1 inch apart.

Place the cookies in a preheated 300°F (150°C) oven. Immediately reduce the temperature to 250°F (120°C). Bake for 25 minutes, then turn the oven off without opening the door. Leave the cookies inside to cool and dry for 2–3 hours, or overnight.

When ready, the cookies should be crisp on the outside and light, airy, and slightly chewy on the inside. If the centers remain soft, allow them to sit in the turned-off oven for an additional hour.