In a small bowl, beat the heavy cream and rum extract until soft peak form. Set aside.
In a medium bowl, beat together the mascarpone cheese, sugar and vanilla. Fold in the whipped cream.
Cut the ladyfingers in half and dunk them in the espresso. Place a layer of ladyfingers in the bottom of 4 glasses. Spoon half of the cheese mixture over the ladyfingers. Top with another layer of ladyfingers and remaining cheese mixture. Top with remaining ladyfingers. Sift the cocoa on top and garnish with berries.