In a shallow dish, combine the strong brewed coffee and coffee liqueur (if using). Set aside.
In a large mixing bowl, beat the heavy cream, powdered sugar, and vanilla extract until stiff peaks form. Set aside.
In a separate bowl, combine the ricotta cheese, mascarpone cheese, and ½ cup unsweetened cocoa powder. Mix until smooth and well combined.
Gently fold the whipped cream into the ricotta mixture until fully incorporated.
Dip each ladyfinger into the coffee mixture for a few seconds, making sure they are fully soaked but not soggy.
Arrange half of the soaked ladyfingers in a single layer at the bottom of a 9x9-inch baking dish.
Spread half of the chocolate ricotta filling over the ladyfingers, smoothing it out evenly.
Sprinkle half of the finely chopped dark chocolate (or mini chocolate chips) over the filling.
Repeat the layers with the remaining soaked ladyfingers, chocolate ricotta filling, and chopped dark chocolate.
Cover the dish with plastic wrap and refrigerate for at least 4 hours, or overnight, to allow the flavors to meld together.
Before serving, dust the top of the tiramisu with unsweetened cocoa powder and garnish with dark chocolate shavings.