Soak the gelatin sheets in a bowl filled with cold water. Take a spring form pan, remove the bottom and place the expandable part on a platter. Dampen (do not soak) the ladyfingers with blueberry juice. Place the lady fingers in a tight ring and cover also the bottom of the platter, creating the base of the cake. Whip the cream and stir in gently the yogurt, adding some icing sugar. Place the gelatin in a small pot with a some water at medium-low heat and stir until the gelatin melts, then add it to the whipping cream. Spread half of the cream on the lady fingers, then continue to alternate a layer of dampened ladyfingers and one of cream, end with a layer of cream. Ultimately smooth the top with a rubber spatula. Decorate with blueberries and chill for at least 5 hours. Open and remove gently the spring form pan using a knife. Serve cold.