Combine sugar, buttermilk, and baking soda in a heavy 5 quart pot. With a wooden or plastic spoon, stir this mixture constantly on high just until it begins to boil. Reduce the heat to medium and continue to stir constantly. The mixture will rise and then fall back down. Continue to stir constantly until the mixture turns light brown and reaches a soft-ball stage approximately 15 to 20 minutes. (Drop a small amount of mixture into a bowl of water to test for soft ball stage. A candy thermometer can also he used to test for the soft ball stage of 234F.) Remove the pot from the heat after the mixture reaches the soft-ball stage. Add the pecans and vanilla. Stir the mixture until it starts to lose its gloss. At this point, quickly spoon out the mixture onto aluminum foil to your desired size. Let the pralines cool and then remove them from the foil.
Serves 2 dozen.
Cajun Country -- New Iberia, Louisiana