This pie is a glorious muddy explosion of chocolate goodness in light-as-a-feather pastry. It's adapted from a Pithivier recipe in Stephanie Alexander's The Cook's Companion.
Note We prefer to use Carême butter puff pastry. Alternatively, buy a 750gm block of butter puff pastry from your local pâtisserie and roll into two 375gm, 4mm-thick squares. Use a good-quality chocolate such as Lindt or Valrhona.