"This recipe does not require the traditional marscapone cheese, which can be both expensive and difficult to find. Actual preparation time is short, but as it must 'age' for at least 10 to 12 hours, this is a dessert best prepared a day ahead of time.
Dust with unsweetened cocoa powder."
Beat cream and 3 tablespoons sugar together in a bowl using an electric mixer until stiff peaks form. Refrigerate until ready to use.
Beat ricotta cheese, sour cream, and sugar together in a bowl. Fold in the whipped cream gently; add rum.
Pour coffee into a bowl. Dip the ends of half of the ladyfingers in the coffee. Arrange ladyfingers dipped side-down into a single layer in a 2- to 2 1/2-inch deep rectangular serving dish. Spread half of the ricotta-cream mixture on top. Repeat dipping and arranging the remaining half of the ladyfingers; spread the remaining ricotta-cream mixture on top. Cover with plastic wrap; refrigerate until fully chilled, 10 to 12 hours.