Preheat the oven to 300 F (150 C).
Prepare 4 baking sheets by lining them with parchment paper.
Finely grind the almond powder and 250 g of powdered sugar, this mixture is called tant pour tant.
Sift this mixture and remove the pieces of almond powder that are too big to pass through the sieve.
Add the remaining powdered sugar, 200 g, and cocoa, then mix well.
Beat the egg whites and add sugar in 2 to 3 times.
Pour the dry ingredients over the beaten egg whites and mix using a spatula, making sure to scrape the bowl.
Macaronage, this is the moment when you need to check if you get a ribbon.
Pour the batter into a pastry bag.
Form squares of batter on the parchment paper.
Let it rest for 30 minutes.
Bake for 15 to 20 minutes.
After baking, slide the parchment paper onto a cold surface and let it cool before removing the shells.
Store in an airtight container in the refrigerator, you can also freeze them.
In a thick-bottomed saucepan, pour the cream and bring to a boil over medium heat.
While the cream is heating up, melt the chocolate in a medium bowl and weigh the speculoos paste.
When the liquid is hot, pour half of it over the chocolate and let it melt for about 30 seconds.
Starting from the center, mix everything using a wooden spoon to incorporate the cream.
Add the remaining cream and speculoos paste and continue to stir gently until the ganache is smooth and shiny.
Cover with plastic wrap and let the ganache set in the refrigerator or at room temperature.