Line a large baking sheet with parchment paper.
In a 2 to 3-quart saucepan, combine the granulated sugar, water, light corn syrup, and salt. Attach a candy thermometer to the side of the pan.
Cook the mixture over medium heat, stirring until the sugar dissolves. Continue to cook, without stirring, until the thermometer registers 260°F (127°C).
While the syrup heats, add the room-temperature egg whites to the bowl of a stand mixer fitted with the whisk attachment. When the syrup reaches about 250°F (121°C), begin beating the egg whites on high speed until stiff peaks form.
Once the syrup reaches 260°F (127°C), remove it from the heat. With the mixer on high speed, very slowly and carefully pour the hot syrup in a thin, steady stream down the side of the bowl into the egg whites.
Continue beating on high speed until the mixture becomes very thick, loses its glossy sheen, and starts to hold its shape, about 6 to 10 minutes. The candy should pull away from the sides of the bowl.
Turn off the mixer and quickly stir in the vanilla extract and toasted pecans.
Working fast, use two buttered spoons to drop rounded tablespoon-sized mounds of the candy onto the prepared baking sheet.
Allow the candy to set at room temperature until it is firm and no longer sticky to the touch. This can take anywhere from 2 hours to overnight, depending on humidity.