PREHEAT oven to 350°F Grease 8-inch-square baking pan.
COMBINE flour, cocoa and salt in small bowl. Beat butter, granulated sugar and brown sugar in large mixer bowl until creamy. Add 2 eggs, one at a time, beating well after each addition. Add vanilla extract; mix well. Gradually beat in flour mixture. Reserve 3/4 cup batter. Spread remaining batter into prepared baking pan. Sprinkle nuts and white morsels over batter. Drizzle caramel topping over top. Beat remaining egg and reserved batter in same large bowl until light in color. Stir in semi-sweet morsels. Spread evenly over caramel topping.
BAKE for 30 to 35 minutes or until center is set. Cool completely in pan on wire rack. Cut into squares.