Add brown sugar, cook over med/low heat for 2 minutes, stirring constantly.
Add cream, continue cooking and stirring occasionally until mixture boils. Boil for 1-1 ½ minutes, stirring occasionally.
Remove from heat, cool until lukewarm (you can put in a sink of cold water).
You can beat by hand OR we like to dump this mix into a stand mixer, add vanilla and beat, then add icing sugar 1 cup at a time. Then beat vigorously for 2-3 minutes by hand or 1-2 minutes in mixer. It will have lightened in colour.
Stir in nuts.
Spread into 8" square pan that is buttered or lined with parchment paper.