01 - Line two baking sheets with parchment paper or silicone mats.
02 - In a heavy-bottomed saucepan over medium heat, combine granulated sugar, brown sugar, milk, butter, and salt. Stir constantly until butter melts and mixture comes to a boil.
03 - Attach a candy thermometer to the pan. Continue stirring and cook until the mixture reaches 238°F (soft-ball stage), about 8–10 minutes.
04 - Remove from heat; immediately stir in pecan halves and vanilla extract. Continue stirring vigorously by hand for 2–3 minutes, until mixture thickens and becomes creamy but is still pourable.
05 - Quickly drop tablespoon-sized mounds onto prepared baking sheets, spacing them apart.
06 - Allow pralines to cool and set completely at room temperature for about 20 minutes before serving or storing.