1. Heat oven to 350°F. Grease 13x9x2 baking pan.
2. Combine melted butter, sugar, eggs and vanilla in large bowl; beat well. Add flour, cocoa and milk; beat until blended. Stir in 1 cup nuts. Pour into prepared pan.
3. Bake 25 to 30 minutes or just until edges begin to pull away from sides of pan. Cool completely in pan on wire rack.
4. Melt 1/2 cup butter and peanut butter chips in medium saucepan over low heat, stirring constantly. Add sweetened condensed milk, stirring until smooth; pour over baked layer.
5. Place chocolate chips in small microwave-safe bowl. Microwave at MEDIUM (50%) 45 seconds; stir. If necessary, microwave at MEDIUM an additional 15 seconds at a time, stirring after each heating, just until chips are melted when stirred. Drizzle bars with melted chocolate; sprinkle with remaining 1/4 cup nuts. Refrigerate 1 hour or until firm. Cut into bars. Cover; refrigerate leftover bars. Makes 24 to 36 bars.