Heat oven to 400° F.
Cut the puff pastry into 4 squares. Line 4 cups of a muffin tin with the squares, allowing the corners to stick out.
In a small bowl, combine the apple, walnuts, and brown sugar. Divide the mixture among the puff pastry squares and bake until the crusts are golden brown, 22 to 25 minutes. Let cool for 10 minutes before removing from the tin.
Meanwhile, in a medium bowl, beat the cream and confectioners' sugar until soft peaks form. Serve with the tarts.
super delicious! this was a huge hit with my friends, and pretty easy to make too.