In the top of a double boiler over simmering water, melt semisweet chocolate. Let cool completely and set aside.
To make the zabaglione, using a hand mixer, beat the egg yolks with sugar in the top pan of a double boiler until frothy and light. Add 1 cup of wine, place over gently simmering water, and whip until the mixture begins to thicken. Do not let it boil. Remove from heat, fold in the cooled chocolate, and let cool completely.
Beat the egg whites until stiff peaks form. Using a spatula, fold it into the cooled zabaglione.
Stir together the espresso and mascarpone cheese and set aside.
Whip the heavy whipping cream until stiff peaks form. (For a sweeter whipped cream, feel free to add 1 Tbsp. of powdered sugar here.)
Dip half of the ladyfingers into the remaining wine and arrange them on the bottom of a 9-inch round dish. Cover the ladyfingers with half of the mascarpone mixture, then half of the zabaglione, then half of the whipped cream. Repeat the layers of ladyfingers dipped in wine, mascarpone cheese mixture, zabaglione, and whipped cream. At this point, the tiramisù may be refrigerated 12-24 hours prior to serving.
Sprinkle the instant coffee and sweet ground chocolate on top just before serving.