Combine the sugar, brown sugar, corn syrup, butter, salt, and condensed milk in a heavy saucepan over medium heat. With a wooden spoon, stir until the sugar dissolves. Continue to cook, stirring, until smooth and light brown, about 8 minutes. Add the vanilla and pecans and continue to cook, stirring, until the mixture reaches 234º to 240ºF. on a candy thermometer or the soft ball stage, that is, when a bit dropped into cold water forms a soft ball that flattens.
Remove from the heat and drop by the spoonful onto wax paper. Let cool. Remove from the paper with a thin knife.
Pralines can be stored in an airtight container at room temperature for up to 2 weeks.
Yield: about 1 1/2 dozen