Prepare the Caramel Layer:

1. Make the Caramel Sauce: If you’re using homemade caramel, prepare it by melting ¼ cup sugar in a saucepan over medium heat, stirring until golden and smooth. Add a pinch of salt if desired, and set aside to cool slightly.
2. Set Aside: Allow the caramel sauce to cool to room temperature before using in the tiramisu.

Prepare the Chocolate Mousse:

3. Melt the Chocolate: In a heatproof bowl, melt the dark chocolate using a microwave or a double boiler. Stir until smooth, and set aside to cool.
4. Whip the Cream: In a large mixing bowl, whip the heavy cream with an electric mixer on medium-high speed until soft peaks form.
5. Mix Mascarpone and Sugar: In a separate bowl, whisk together the mascarpone cheese, powdered sugar, and vanilla extract until smooth and creamy.
6. Combine the Chocolate and Cream: Gently fold the melted chocolate into the mascarpone mixture, followed by the whipped cream. Stir until fully combined.

Prepare the Coffee Mixture:

7. Brew the Coffee: Brew a strong cup of coffee or espresso and let it cool to room temperature.
8. Add Liquor (Optional): If using, stir the dark rum or coffee liqueur into the cooled coffee.

Assemble the Tiramisu:

9. Soak the Ladyfingers: Quickly dip each ladyfinger into the coffee mixture, ensuring they’re not overly soaked. Layer the dipped ladyfingers in the bottom of a 9×9-inch or similar-sized serving dish.
10. Layer the Caramel and Mousse: Spread a thin layer of caramel sauce over the ladyfingers, followed by half of the chocolate mousse, smoothing it out with a spatula.
11. Repeat the Layers: Add another layer of dipped ladyfingers, drizzle with more caramel sauce, and top with the remaining chocolate mousse. Smooth out the top layer.

Chill and Serve:

12. Chill the Tiramisu: Cover the dish with plastic wrap and refrigerate for at least 3.5 hours or overnight to allow the flavors to meld.
13. Garnish and Serve: Just before serving, dust the top with cocoa powder and garnish with chocolate shavings or curls for an extra touch of elegance.