Preparation: Lightly grease a 9×13-inch baking dish, setting it aside for later use.
First Sugar Melt: In a saucepan with a thick bottom—if available—melt 2 cups of sugar over low heat. Stir frequently and ensure the sugar is fully liquefied, which should take approximately 20 minutes.
Creamy Fusion: While the initial sugar portion is dissolving, combine the remaining 4 cups of sugar and heavy cream in a large saucepan or Dutch oven. Simmer this mixture on low heat.
Merge the Sugars: Once the sugar in your smaller saucepan is thoroughly melted, pour it into the large saucepan, stirring continuously.
Achieving Softball Stage: Crank up the heat to medium and continue to cook the mixture until it reaches a temperature of 244°F, or the softball stage.
Baking Soda Incorporation: Remove your saucepan from heat. Stir in the baking soda until it is fully assimilated into the mixture.
Flavor Infusion: Add in the unsalted butter and vanilla extract. Stir the concoction until the butter is fully melted and the mixture turns smooth.
Rest & Settle: Allow the mixture to rest for a 20-minute interlude.
Nutty Finale: Once the mixture has rested, stir in your choice of chopped walnuts or pecans until the glossy sheen vanishes. Transfer this to your pre-prepared baking dish.
Final Touch: Let the candy cool for 1-2 hours, or even overnight if you can resist the temptation. Slice into bite-sized squares and indulge!