Start by brewing 1 cup of strong coffee or espresso and allow it to cool completely. Once cooled, mix in ½ cup Kahlua and ½ cup sugar until the sugar dissolves. Set this coffee mixture aside—this is what you’ll use to dip your ladyfingers.
In a medium bowl, whisk together 3 large egg yolks and sugar until the mixture turns pale and slightly thickened, about 3-5 minutes by hand or 2-3 minutes with an electric mixer.
Fold the softened 1 cup mascarpone cheese and 1 teaspoon vanilla extract into the egg yolk mixture until smooth and well combined.
In a separate bowl, whip 1 cup heavy cream until soft peaks form. Gently fold the whipped cream into the mascarpone mixture, combining carefully to maintain a light, airy texture.
Quickly dip each ladyfinger into the coffee mixture—just a second or two per side so they don’t get soggy—and lay them in a single layer in your dish. Spread half of the mascarpone cream over the ladyfingers. Drizzle half of the melted dark chocolate over the cream, swirling gently with a spatula.
Repeat the process: dip ladyfingers in coffee mixture and layer on top of the cream. Finish with the remaining mascarpone cream and drizzle the rest of the melted chocolate on top.
Using a fine mesh sieve, dust the top generously with unsweetened cocoa powder. Cover the tiramisu and refrigerate for at least 4 hours, or overnight for the best flavor and texture.