1. Heat oven to 375 degrees. Whisk to combine sugar with 1/4 cup water in a small saucepan set over medium heat. Without stirring, cook mixture until dark amber in color, 10 to 12 minutes. Pour 1 tablespoon caramel into the bottom of a standard 10 1/2-by-13 1/2-inch muffin tin. Add 1 teaspoon butter to each muffin cup. Set aside.

2. Combine cranberries and walnuts in a small bowl. Using a teaspoon, fill apple's center with cranberry mixture; repeat with remaining apples. Place apples, stem-side down, into caramel.

3. Meanwhile, on a lightly floured surface, roll out puff pastry to a 12-inch square. Using a 2 1/2-inch cookie cutter, cut out twelve circles. Place puff-pastry circles over apples, tucking pastry around apples. Bake at 375 degrees until pastry is golden brown and puffed, 30 to 35 minutes. Turn out immediately onto a Silpat-lined baking sheet. Serve immediately.