PREHEAT oven to 350° F. Grease 13 x 9-inch baking pan.
MELT 1 cup morsels and butter in large, heavy-duty saucepan over low heat, stirring constantly until smooth. Remove from heat; stir in eggs. Add flour, sugar, baking soda and vanilla extract; stir well.
SPREAD batter into prepared baking pan; sprinkle with remaining morsels and walnuts.
BAKE for 20 to 25 minutes or until wooden pick inserted in center comes out slightly sticky.
MICROWAVE caramels and milk in small, microwave-safe bowl on HIGH (100%) power for 1 minute; stir. Microwave at additional 10- to 15-second intervals, stirring until melted. Drizzle over warm brownies. Cool in pan on wire rack.