Meanwhile combine brown sugar, 2/3 cup whipping cream and butter in sauce pan. Cook over medium heat stirring constantly until mixture comes to a boil. Reduce heat. Simmer stirring constantly for 1 minute. Cool to room temperature.
Drizzle 2 tablespoons sauce over each layer.
Place remaining sauce in bowl. Add powdered sugar. Beat on high til smooth, 3 minutes. Add enough whipping cream for spreading consistancy.
Place 1 layer on plate. Spread with 3/4 cup frosting. Sprinkle with chopped pecans.
Top with second layer. Spread top and side with remaining frosting. Arrange pecan halves on top.