Have ready a wooden spoon, candy thermometer, pastry brush and cup of hot water to brush down sugar crystals from the sides of the pan. Also, have handy 2 tablespoons to use for dipping and dropping the candy.
Line 3 baking sheets with parchment paper or foil, butter generously; set aside. (Don't use wax paper; the candy will stick to it.).
Combine in a heavy 3-quart saucepan the sugar, baking soda, buttermilk, corn syrup, ginger, butter, rum or vanilla extract. Place the pan on medium-high heat and bring the syrup to a boil, stirring until the sugar is completely dissolved, for 6 to 8 minutes.
Then, cover the pan and boil the syrup without stirring for 3 minutes. (Stirring will make the mixture grainy.) Remove the cover. Dip the pastry brush into the water and brush down the sides of the pan. Attach the candy thermometer to the inside of the pot.
Cook the syrup without stirring until it reaches 225 degrees, frequently brushing down the pan with the damp brush.
Quickly scatter the pecans or walnuts over the syrup and continue cooking until the syrup reaches 236 degrees or the soft ball stage and is deep amber in color. Watch carefully, because the candy cooks quickly at this point and can burn.
Remove the thermometer. Add the rum or vanilla extract and butter and swirl the pan until combined. Then move quickly to the work area.
Using the 2 tablespoons and, working quickly, scoop the candy with 1 tablespoon and use the second spoon to push the candy onto the baking sheet, dropping the candies about 2 inches apart.
Allow the pralines to cool and let stand until firm and crunchy and the consistency of hard fudge, at least an hour or longer.
The pralines can be stored in airtight containers for a week or so.