Boil 3 cups sugar with cream and rind in a large saucepan until a small amount of mixture forms a soft ball when dropped into very cold water (236Â°F.
on a candy thermometer).
Meanwhile, melt remaining 1 cup sugar in heavy skillet, stirring until it reaches the brown caramel stage.
When both mixtures are ready, carefully add the caramel to the first mixture, stirring with a long spoon.
Test for soft ball and if done, remove and cool to lukewarm.
If not done, remove and cook to soft-ball stage.
Add vanilla, nuts, and salt, and beat until stiff and creamy.
Drop onto a buttered cookie sheet.
Let cool before removing from sheet.