Bring the heavy cream to a boil and pour it over chocolate chips. Stir with a spoon until homogeneous and smooth. Stir in the cognac if desired.
Let the ganache mixture cool down while you are working on the other steps.
Toast the hazelnuts in the oven at 350F (180C) for 10 minutes. Take the nuts out of the oven and let them cool down. Rub the nuts between your palms to remove the skins.
Pulse the nuts and sugar in a food processor (or a blender) until the nuts are finely ground.
Whip the egg whites with a pinch of salt to hard peaks.
Combine the nut mixture, cocoa powder, whipped egg whites the honey in a bowl. Mix until the mass looks homogeneous.
Using a pastry bag with a large star tip, pipe the batter onto a large (21" x 15") baking sheet lined with parchment paper. Make the batter disks about 1.5" in diameter. The total will be about 48-52 disks.
Bake the pastry shells at 400F (200C) for 10-12 minutes. Take them out of the oven and let them cool down.
Using a pastry bag with a medium star tip, pipe the ganache on one half of the pastry shells and assemble them into sandwiches.
Gently transfer to a serving platter and let the ganache set before serving, about an hour or so.