Heat oven to 250°F. Line two baking sheets with parchment paper.
Wipe the mixing bowl and whisk with a little vinegar or lemon juice to remove any grease; dry well.
Beat egg whites and salt on medium speed until foamy. Sprinkle in cream of tartar; beat to soft peaks.
Increase to medium-high and slowly rain in the sugar, 1–2 tablespoons at a time, until glossy stiff peaks form.
Beat in vanilla just to combine, then gently fold in the chopped pecans with a spatula.
Spoon heaping tablespoons of meringue onto the sheets, spacing about 1 inch apart.
Bake 50–55 minutes, until set and dry to the touch. Turn off oven and leave cookies inside 15–20 minutes to dry further.
Cool completely on the sheets, then transfer to an airtight container.