Start by sifting together the powdered sugar, powdered almonds, and cocoa powder into a large mixing bowl. Set aside.
In another clean bowl, whip the egg whites with an electric mixer until frothy. Gradually add granulated sugar, continuing to whip until stiff peaks form, about 5 to 7 minutes.
Gently fold the dry mixture into the egg whites without deflating the meringue until just combined.
Transfer the batter into a piping bag fitted with a round tip. Pipe small circles on a baking sheet lined with parchment paper.
Allow the piped macarons to rest at room temperature for 30 to 60 minutes until a skin forms on the surface.
Preheat your oven to 300°F (150°C). Bake the macarons for about 15-20 minutes, rotating halfway through. They should be firm to the touch.
Prepare the ganache by combining heavy cream and light corn syrup in a saucepan over medium heat. Simmer, then remove from heat and add chopped chocolate and butter, stirring until smooth. Mix in prunes and Armagnac.
Once cooled, pair macarons by size. Pipe ganache on one macaron and sandwich with another.
For best flavor, refrigerate the assembled macarons for at least 24 hours before serving.
