1Heat oven to 350°F. Place paper baking cup in each of 24 regular-size muffin cups.
2In large bowl, beat cake mix, water, oil and eggs with electric mixer on low speed 30 seconds, then on medium speed 2 minutes. Stir in syrup and 1 cup of the chopped walnuts. Divide batter evenly among muffin cups.
3Bake 15 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes; remove from pans to cooling racks. Cool completely.
4In medium bowl, beat mascarpone cheese, cream cheese, powdered sugar and maple flavor with electric mixer on low speed until blended, then on high speed until frosting is smooth and spreadable. Frost cupcakes. Sprinkle evenly with remaining 1/2 cup chopped walnuts.