Place the walnuts in the bowl of a food processor and stir. Then add flour, butter, a pinch of salt, sugar and stir. Then, break the egg into the resulting mass, pour the vanilla essence and stir a little more. Knead the dough until it sets well. Cut the dough into two equal pieces and shape them into slightly flattened balls. Wrap them in cling film and refrigerate for 30 minutes.

Before removing the dough from the refrigerator, transfer the berries to a bowl, add the cornstarch, sugar, vanilla essence and stir, but don't crush the berries.

Take a piece of dough out of the fridge and spread it in a circle with a diameter of 30-35 cm. Place the dough on a baking sheet lined with parchment paper. Spread ½ of the amount of berries in the middle of the circle, leaving an empty edge of about 7-8 cm. Then pull the edges over the filling, but in such a way that the middle with the berries remains uncovered.

Grease the edges with egg yolk and sprinkle with chopped walnuts on top.

Bake the biscuits in the preheated oven at 190° C for 25-30 minutes or until the top is of nice brown color. Serve both hot and cold biscuits.