1. Heat oven to 350°F. Combine pretzels and melted butter in small bowl; press evenly into bottom of ungreased 13x9x2-inch baking pan.
2. Place sweetened condensed milk and unsweetened chocolate in small microwave-safe bowl. Microwave at MEDIUM (50%) 1 minute; stir. If necessary, microwave at MEDIUM an additional 15 seconds at a time, stirring after each heating, until mixture is melted and smooth when stirred. Carefully spread over pretzel layer in pan. Top with marshmallows, coconut and pecans; press firmly down onto chocolate layer.
3. Bake 25 to 30 minutes or until lightly browned; cool completely in pan on wire rack.
4. Melt semi-sweet chocolate and shortening in small microwave-safe bowl at MEDIUM (50%) 1 minute or until melted when stirred; drizzle over entire top. Refrigerate 15 minutes or until glaze is set. Cut into bars. Makes about 24 bars.