Combine 4 cups sugar and cream in a heavy 4-quart saucepan.
Melt 2 cups sugar in a heavy 10-inch skillet over medium heat.
Stir sugar constantly until it begins to melt.
Heat sugar-cream mixture over medium heat.
Continue melting sugar in skillet, stirring and watching closely so it does not scorch.
As soon as it is completely melted, pour liquid sugar in a thin stream into boiling sugar-cream mixture, stirring constantly.
Do not let sugar remain over heat after completely melted; this will produced a scorched taste.
Cook combined mixtures to 246.
Remove from heat and add baking soda and butter.
Stir in and let candy stand for 30 minutes.
Stir to mix; pour into buttered 9-inch square pans.
Cool slightly and cut into squares.