Grease a 9x13-inch baking dish and set aside.

Melt 2 cups of sugar in a small saucepan over low heat, stirring often, until completely melted.

In a large saucepan, combine the remaining 4 cups of sugar and heavy cream. Simmer over low heat.

Stir the melted sugar into the large saucepan and cook to 244°F (softball stage).

Remove from heat and stir in baking soda, butter, and vanilla. Let rest for 20 minutes.

Stir in nuts, pour into prepared baking dish, and spread evenly.

Cool for 1–2 hours or overnight. Cut into squares to serve.