1. Combine coffee and 4 tablespoons of the rum in a pie plate or wide baking dish and set aside to cool.
2. Make mascarpone cream. In a medium bowl, combine 1/2 cup of the heavy cream, remaining 2 tablespoons of the rum, sugar, salt, and mascarpone cheese. Mix well and set aside.
3. Pour remaining 1 cup cream into a large bowl and beat with an electric mixer until it holds stiff peaks, about 5 to 7 minutes. Be careful not to overbeat. Using a rubber spatula, gently fold about 1/3 of the whipped cream into the mascarpone mixture to lighten, then gently fold in remaining whipped cream until mixture is uniform. Set aside.
4. Assemble tiramisu. Working one at a time, roll half the ladyfingers very quickly in coffee mixture and arrange in a snug single layer in a 9-by-13 inch glass or ceramic baking dish, breaking or trimming ladyfingers as necessary to fill the dish. Spread half the mascarpone cream evenly over ladyfingers, using a rubber spatula to work mixture into corners of dish and to smooth surface. Sprinkle half the grated chocolate evenly over the mascarpone, then repeat dipping and arranging remaining ladyfingers over the mascarpone and chocolate layer. Spread remaining mascarpone evenly over the second layer of ladyfingers, smooth top with spatula, and sprinkle with remaining chocolate.
5. Cover tightly with plastic wrap and refrigerate to set, 6 to 24 hours. At serving time, remove plastic wrap, place cocoa powder in a fine mesh strainer, and sprinkle evenly over top of tiramisu. Wipe edges of dish clean, and serve.
Source: Hannaford fresh Magazine, November - December 2007