In a medium saucepan, combine brown sugar, cream and butter. Stir until dissolved. Heat to between 234 and 240 degrees F (112 to 116 degrees C), or until a small amount of syrup dropped into cold water forms a soft ball that flattens when removed from the water and placed on a flat surface. Remove from heat and stir vigorously until mixture loses its gloss, or process in a food processor 30 seconds. Quickly stir in vanilla and nuts and spread into a 9x9 inch dish. Chill before cutting into squares.
