Thaw the puff pastry for about 45 minutes on counter until soft enough to roll out, but still very cold.
Meanwhile, cut a heart template from paper that is 11-12 inches wide.
Preheat oven to 400 degrees.
Unfold one piece of pastry and roll it out slightly until it's just bigger than the heart.
Use a pizza cutter to cut out the heart, and repeat with the other pastry.
Place one heart on a cookie sheet liner. Spread it with 1/2 cup nutella. Top with the other heart.
Make cuts from the edge of the heart almost to the middle, about 1 inch apart, all the way around the heart. Leave the pieces attached in the middle.
Twist each piece as shown in the blog post.
Beat one egg with 1 tablespoon water and brush over surface of heart.
Bake 20 minutes until puffed and golden brown.
Sprinkle with powdered sugar and drizzle with jam. Serve warm or at room temperature.
Pastry tastes best if eaten within a few hours.