Preparation

To make the crêpes

• Whisk the eggs with the cold milk, sparkling water, and salt. Whisking steadily, sift the flour over the egg mixture in a gradual but steady “rain” to make a smooth batter. Let sit for 20 min. and then add more sparkling water if necessary to get the consistency of heavy cream.
• Heat a 6- to 8-inch crêpe or omelet pan (nonstick is fine but not necessary). Brush the pan with melted butter. Tilting and turning the pan with one hand, pour in just enough batter to cover the pan’s surface, about 3 Tbs. Let the crêpe cook until golden on the underside, 1 to 2 minutes. (don’t undercook them) and then flip or turn the crêpe with a small spatula or your fingers to cook the other side until just set, about 30 seconds more. The side cooked first will be prettier and should be the outer side when filling the crêpes.
• Adjust the heat so you get a definite sizzle when adding the batter, and thin the batter if the crêpes are too thick and flabby. Stack the finished crêpes on a plate as you go. Cover with plastic and refrigerate until using, up to three days ahead. You can also wrap the crêpes tightly and freeze them (put a piece of waxed paper between each one for easier separation).

To make the filling

• Heat the rum and soak the raisins in it while assembling the other ingredients. In a small saucepan, bring the cream and sugar to a boil, stirring, and add the walnuts, candied orange peel (or zest), cinnamon, cocoa powder, and salt. Bring back to a boil, stirring, and cook until the liquid has reduced almost completely but the nuts are still well coated and glossy, about 3 minutes. Stir in the raisins and rum and cool. You can make this filling a day or two ahead and refrigerate it until time to use.

For the chocolate sauce

• In a medium saucepan, combine the cocoa powder, sugar, flour, and salt. Whisking steadily, slowly pour in the milk to make a smooth paste. Bring the mixture to a boil and cook about 30 seconds to cook off the raw floury taste, and then remove from the heat and add the chopped chocolate. Stir until smooth, cover loosely with plastic, and cool to room temperature, stirring occasionally to help it cool and prevent a skin from forming. Just before serving the crêpes, whip the cream until it just forms soft peaks. Stir about one-quarter of the whipped cream into the chocolate to lighten it, and then carefully fold the rest of the whipped cream into the sauce until well blended.

To finish

• Spread about 2 Tbs. of the filling on the underside of a crêpe (reheat the filling slightly if it’s cold from the refrigerator). Fold the crêpe in half, and then in half again to make a quarter circle. Repeat with the remaining crêpes, dividing the filling evenly. You can do this early on the day of serving and just keep the filled crêpes covered at room temperature.
• In a large frying pan, heat 2 Tbs. of butter over medium heat until sizzling. Add the filled crêpes to the pan without crowding them (do this in batches if you need to). Cook the crêpes until warmed through and browned on each side, about 1 min. per side. Add more butter if necessary to the pan during cooking.
• Arrange 3 crêpes on each plate and drizzle a generous ribbon of chocolate sauce on top, passing more sauce at the table. Serve immediately.