Each of these buttery, flaky packets bears a delicoius surprise: a layer of Nutella, which turns wonderfully melted during baking. Before baking, the pastries are brushed with beaten egg, to encourage browning; be careful not to let the egg wash drip over the sides, or it will inhibit rising. A sprinkling of sugar provides extra crunch. These are best served hot, but not too hot: that chocolatey filling can burn the tongue if not careful.