Preheat the oven to 400ºF.
Use the bottom of a 9-inch false-bottomed tart or springform cake pan to trace and cut out a 9-inch circle on the puff pastry. Replace the bottom in the pan, place the round of pastry dough onto it, and brush some of the beaten egg over it.
Using a small sharp knife or pastry cutter, cut out a 1/2-inch strip of dough around the original circle and place this strip in the tart pan on top of this bottom crust around its edge to form a lip or border. Use a knife or fork to crimp a design in this border. Perforate the bottom crust all over with the tip of a knife.
Sprinkle the bottom crust with 1 tablespoon of the sugar, 1/2 teaspoon of the cinnamon, and 1/4 teaspoon of the nutmeg. Dot it with 1 tablespoon of the butter. Meanwhile, in a small saucepan over low heat, melt the remaining 1 tablespoon butter.
Toss the apple slices with the remaining 2 tablespoons granulated sugar, 3/4 teaspoon cinnamon, a pinch of nutmeg, and the melted butter. Blend until the mixture is thoroughly incorporated.
Arrange the apple slices like spokes on top of the crust, without covering the crimped border. Pour the accumulated juices from the bowl over the apples. Bake until the pastry is brown and puffy, for about 40 minutes. Remove the tart from the oven allow it to cool slightly. Remove it from the pan to a serving dish.
To serve, sift the confectioners’ sugar over the tart, mound the whipped cream in the center, and cut into wedges.
Yield: one 9-inch tart