In a large bowl, whisk flour, sugar, baking powder and salt. Transfer to a 1-qt. resealable plastic bag. In a snack-size plastic bag, combine brown sugar, walnuts and cinnamon. Store bags in a cool, dry place or in freezer up to 3 months., To prepare muffins: Preheat oven to 350°. Place flour mixture in a large bowl. Cut in shortening until crumbly. In a small bowl, whisk egg and milk until blended. Add to flour mixture; stir just until moistened. In a small bowl, mix brown sugar mixture with melted butter., Fill greased or paper-lined muffin cups half full. Sprinkle with brown sugar mixture. Bake 18-22 minutes or until a toothpick inserted in center comes out clean. Cool 5 minutes before removing from pan to a wire rack. Serve warm.