Line the bottom of an 8x8x2-inch baking pan with some of the ladyfingers, cutting to fit as necessary. Drizzle half of the espresso over ladyfingers;set aside.
In a medium mixing bowl, beat together the mascarpone cheese, whipping cream, powdered sugar, and vanilla with an electric mixer just until stiff peaks form. Beat in the chocolate liqueur until just combined. Spoon half of the mascarpone mixture over ladyfingers, spreading evenly. Sprinkle white chocolate and bittersweet chocolate over the mascarpone mixture. Top with another layer of ladyfingers (reserve any remaining ladyfingers for another use). Layer with remaining espresso and mascarpone cheese mixture.
Cover and chill for 6 to 24 hours. Sift cocoa powder over top of dessert. If desired, garnish with cocoa beans.