Combine buttermilk and soda in a large pan.

Let the mixture stand for 3 minutes to react.

Add sugar and butter to the pan.

Cook over medium-high heat, stirring constantly, until the mixture reaches a rolling boil.

Continue boiling and stirring until a small amount of the mixture forms a soft ball when dropped into cold water (soft ball stage).

Remove from heat and let cool to room temperature without stirring.

Once cooled, beat the fudge until it becomes creamy.

Stir in vanilla extract and nuts.

Pour the fudge into a buttered dish and let set.