1. Start by greasing a 9×13 inch baking pan to prevent the candies from sticking.
2. In a heavy-bottomed saucepan, melt 2 cups of sugar over low heat, stirring occasionally. It will take about 20 minutes for it to fully melt and become a golden syrup.
3. Gradually incorporate the remaining sugar and the heavy cream into the melted sugar, stirring continuously until well blended.
4. Raise the heat and cook the mixture until it reaches 244°F (118°C) on a candy thermometer, ensuring it reaches the soft-ball stage.
5. Once the desired temperature is reached, remove the pan from heat and carefully stir in the baking soda. This will help brighten the mixture and create a light texture.
6. Add in the vanilla extract and the unsalted butter. Stir until the mixture is smooth and homogenous.
7. Let the mixture rest for approximately 20 minutes; this step will allow it to thicken slightly.
8. Once it has rested, fold in the chopped pecans until they are evenly distributed throughout and the candy mixture loses its glossy finish.
9. Pour the mixture into your prepared baking pan, spreading it evenly across the surface.
10. Allow the candy to cool completely at room temperature for about 12 hours. Afterward, cut it into squares and enjoy your delicious creations!