Prepare the meringue shells as directed in Steps 1 through 4 in the main recipe.
Spread the almond sponge batter evenly over a half sheet pan (12 x 16 inches/30 x 40 cm) lined with baking paper or a Silpat. Bake at 400°F(205°C) for approximately 6 to 8 minutes or until the top springs back when pressed lightly. Set aside to cool.
Flavor the buttercream with ⅓cup (80ml) kirsch liqueur.
Combine the remaining kirsch liqueur with the water.
Unmold the sponge, remove the paper or the Silpat, and cut out 40 rounds, 2¼ inches (5.6 cm) in diameter, using a plain cookie cutter. Brush the sponge circles generously with the kirsch and water mixture.
To assemble each pastry, spread cherry-flavored buttercream on the top of 2 Japonaise circles and sandwich them together, placing a soaked sponge circle inside. Refrigerate until firm.
Crush the reserved shells, as well as any trimmings from the others, to very fine crumbs. Pass the crumbs through a coarse sifter.
Spread a very thin layer of buttercream on the sides of the chilled pastries. (You can do this faster by holding 2 pastries together while you ice the sides.) Roll the sides in the reserved crumbs to coat them completely, leaving the tops exposed.
Sift powdered sugar over the tops of the pastries, using enough to cover them completely. Use the back of a paring knife or the wire of a hard-boiled-egg slicer to mark the sugar, first in one direction and then at a 45-degree angle, to create a diamond pattern.
Place a small amount of chopped blanched pistachios in the center of each pastry. Store, covered, at room temperature for up to 4 days.