Whip the cream with the sugar until stiff. Gradually stir in the sour cream, créme fraiche and lemon juice. Coarsely chop the cantuccini.
First put 1/3 of the frozen fruit mixture in a glass bowl (you can also use drained canned fruit instead of the fruit mixture, I personally like it better). Spread 1/3 of the cantuccini crumbs on top and spread 1/3 of the cream mixture on top. Repeat this process twice.
Finally, sprinkle with a few cantuccini crumbs. Leave the sour cream dessert covered in the refrigerator for about 3 hours.