Boil 3 cups sugar with the cream in a large saucepan until it forms a soft ball (236°F on a candy thermometer).
Meanwhile melt remaining sugar in heavy skillet, stirring until it reaches the brown-caramel stage.
When both mixtures are ready, carefully add caramel to first mixture, stirring with a long spoon.
Cook to soft-ball stage.
Remove from heat and cool to lukewarm.
Add vanilla, nuts, and salt and beat until stiff and creamy.
Drop on a buttered cookie sheet.
Let cool before removing from sheet.
Makes about twenty 3-inch pralines.