Line a square baking pan (ca.20x20cm) with parchment paper. Line the bottom of the baking pan with butter cookies. In a pot, heat together the milk, butter, sugar and nutella. Stir in the semolina. Lower the temperature and cook, while stirring constantly, until it has a thick porridge consistency. Remove the semolina mixture from the heat and spread evenly on the cookie lined baking pan. Place a second layer of cookies on top of the nutella-semolina and allow to cool for one hour.
Dissolve the potato flour in 50ml of water. In a pot, bring the puréed strawberries, water and sugar to a boil. Remove the pot from the heat. Stir in the potato flour water and mix well. While stirring constantly, bring the complete mixture to a boil. Spread the strawberry mixture evenly on the last layer of cookies and allow to cool.
Prepare the gelatin according to the package instructions. Mix together the yoghurt, heavy cream and vanilla sugar. Whisk together 1 tablespoons of the yoghurt mixture with the hot gelatin. Then mix in the rest of the yoghurt mixture and spread over the strawberry layer. Refrigerate the cake overnight.
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