Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper.

In a bowl, combine almond flour and powdered sugar. In a separate bowl, whisk the egg yolks and 1/4 cup granulated sugar until pale and fluffy. Gently fold in the almond flour mixture and all-purpose flour, followed by the vanilla extract and salt.

In another bowl, beat the egg whites until soft peaks form. Gradually add the remaining 1/4 cup granulated sugar and continue beating until stiff peaks form. Gently fold the egg whites into the almond flour mixture until just combined.

Spread the batter evenly onto the prepared baking sheet and bake for 12-15 minutes or until lightly golden. Allow to cool completely.

For the buttercream, beat the softened butter with 1/2 cup granulated sugar until creamy. Add cocoa powder and 1/2 teaspoon vanilla extract, mixing until smooth.

For the chocolate ganache, heat the heavy cream in a saucepan until just simmering. Pour over the chopped dark chocolate and let sit for a few minutes before stirring until smooth.

To assemble, cut the cooled cake into three equal rectangles. Brush each layer with the coffee syrup (made by combining brewed coffee, coffee liqueur, water, and sugar in a saucepan until dissolved).

Layer one rectangle on a serving platter, spread with a layer of buttercream, then add another rectangle, spread with ganache, and repeat. Top with the final rectangle and cover the entire cake with remaining ganache.

Chill the cake in the refrigerator for at least 2 hours before slicing and serving.