Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

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

In a large mixing bowl, cream the softened butter and granulated sugar together until light and fluffy, about 3-4 minutes.

Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

Gradually add the dry ingredients to the butter mixture, alternating with the buttermilk. Mix until just combined.

Divide the batter evenly between the prepared cake pans. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.

Allow the cakes to cool in the pans for 10 minutes, then transfer them to a wire rack to cool completely.

In a shallow dish, combine the brewed coffee and coffee liqueur (if using). Set aside.

Once the cakes are completely cooled, slice each cake in half horizontally to create four layers.

To assemble, place one layer on a serving plate. Brush generously with the coffee mixture. Spread a layer of mascarpone cheese on top, followed by a layer of whipped cream (whip the heavy cream with powdered sugar until soft peaks form).

Repeat the layering process with the remaining cake layers, brushing each with coffee and adding mascarpone and whipped cream in between.

Once assembled, dust the top with cocoa powder and garnish with dark chocolate shavings if desired.

Refrigerate the cake for at least 2 hours before serving to allow the flavors to meld.