Preheat the oven to 350°F (175°C). Grease and line a 9x13 inch baking pan with parchment paper.

In a medium bowl, whisk together the flour, cocoa powder, and salt. Set aside.

In a large bowl, beat the eggs and granulated sugar together until light and fluffy, about 5 minutes.

Gently fold the dry ingredients into the egg mixture until just combined. Then fold in the melted butter and vanilla extract.

Pour the batter into the prepared baking pan and spread it evenly. Bake for 15-20 minutes or until a toothpick inserted in the center comes out clean. Let it cool completely in the pan.

While the cake is cooling, prepare the ganache. In a small saucepan, heat the heavy cream until it just begins to simmer. Remove from heat and add the chopped dark chocolate. Stir until smooth and glossy. Let it cool slightly.

Once the cake is cool, slice it into three equal layers. Brush each layer with the brewed coffee mixed with coffee liqueur if using.

Place the first layer on a serving platter. Spread a layer of ganache over it, then add the second layer of cake. Repeat the process with the second layer and top with the final layer of cake.

Cover the top and sides of the cake with the remaining ganache. Chill in the refrigerator for at least 2 hours before serving.

For a decorative touch, dust the top with powdered sugar or cocoa powder before slicing.