Blueberries are left at room temperature to thaw. Biscuits are crushed or broken into very small pieces. The soft butter is mixed with biscuits to obtain a homogeneous mixture. In a baking dish (covered with baking paper) is evenly distributed bishkotenata mixture. With slight pressure forming the base of the cake and leave to cool. 10 sheets of gelatin is soaked in cold water for 10 minutes and thawed in a water bath. In a deep bowl whipped cream the feta cheese, yogurt and 1 cup sugar. Add the cooled gelatin and mix. Pour the mixture into cake form, smoothed and cooled until firm. 5 sheets of gelatin is soaked in cold water. Blueberry juice (released on thawing) is mixed with water to give 300 ml liquid. Starch is diluted in a little water. Blueberry juice is heated with 5 tbsp sugar and stirring continuously, add the starch. Boil to compress and cool slightly. In the cooled mixture was added drained gelatin and mix until dissolved. Add blueberries and with the mixture carefully pour the cake. Cool at least 3 hours. Blueberry yogurt, can be replaced with natural yogurt mixed with mashed blueberries or blueberry jam. It is desirable edge of cake to form an oily, it does not stick. Before being ousted edge with knife separates the cake from the sides of the form. The cake is cut with a knife dipped in cold water.