1
Preheat the oven to 170°C. Mix the dry ingredients and add the wet ingredients. Stir to combine. Sprinkle a few tablespoons of coarse flour on the counter, put the dough on it and knead it well with your hands. Divide the dough into two equal parts.
2
Roll out the dough ball on baking paper into a rectangle, 1 mm to 1,5 mm thick. Spread 3 tablespoons of jam over it and sprinkle with 2 tablespoons of ground walnuts. Roll the dough lengthways on both sides towards the centre, leaving a 3 cm gap. Use baking paper to help the dough to roll. Once the dough has been rolled, transfer it and the paper to the baking tray and cut off the top of the paper on both sides. Repeat the same process with the other part of the dough and cover the ''loaves'' to let them rise in a warm place until the filling is ready.
3
Whisk the egg whites with the sugar until thick and stiff. Fold in the ground walnuts with a spatula. Transfer the filling into a piping bag and pipe into the empty space in the centre. Slide the baking tray into the oven and bake for about 30-35 minutes.
4
Sprinkle the cooled pastry with icing sugar and cut into slices as wide as you like.