1. Line 2 rimmed baking sheets with wax paper or foil. Set aside.
2. Combine the buttermilk and baking soda in a medium saucepan over medium heat, and whisk until slightly frothy. Add the sugar, corn syrup and salt. Bring to a boil, stirring, until the sugar is dissolved, watching carefully and adjusting the heat to ensure it does not boil over.
3. Clip on a candy thermometer and cook, stirring occasionally, until the mixture thickens, turns a dark caramel color and reaches the soft-ball stage (the candy thermometer registers 235 to 240 degrees F), 12 to 15 minutes. Remove from the heat and stir in the pecans, butter and vanilla. Using a wooden spoon, beat the mixture vigorously until it lightens in color slightly, thickens and the spoon leaves a trail on the bottom of the pan, 4 to 8 minutes.
4. Working quickly, use 2 spoons to scoop and drop bite-size portions onto the prepared baking sheets. Allow to set at room temperature, about 20 minutes.
NotesCook's Notes: Don't be afraid to use a lot of strength after you remove the mixture from the heat and beat in the pecans, butter and vanilla--it helps to get the cooling process going and incorporates some air to get that slightly fudgy consistency.
As an alternative, instead of chopping and stirring in the pecans, leave them as halves. Spoon the pralines onto the baking sheets and top each one with a pecan half.