Croatian Sand Cookies

Very tasty Croatian shortbread cookies with jam, nuts, and whipped egg white. It has a very interesting name "Grandfather's Mustache".
Ingredients:
- 270-300 grams of flour
- 1 egg
- 100 grams of butter at room temperature
- 60 grams of sugar (in the dough)
- 60 ml of warm water
- 1 teaspoon of baking powder (not heaped)
- a pinch of salt
- a pinch of vanillin
For the filling:
- egg white - 1 piece,
- walnuts - 70 grams
- 1 teaspoon of cocoa
- 150-200 grams of thick jam
- sugar - 1 tablespoon
First, we will make the shortbread dough.
Mix the egg with salt and sugar. Beat a little and add the softened butter. Beat again. Then pour in the water and add vanillin. Mix again. Add the sifted flour, baking powder, and knead a soft dough, which we form into a ball and put in the fridge for 30 minutes.
During this time, you can prepare the nuts. They need to be finely chopped. Preheat the oven to 170 degrees.
Take out our dough and roll it out into a sheet on parchment paper, 25 cm wide, and 4-5 mm thick. To work with the dough more easily, you can sprinkle it with a little flour. Spread the sheet with jam and sprinkle with nuts (50 grams). Start rolling it up, like a kind of roll from both sides alternately towards the center. Leave about 3 cm of space between them (as seen in the photo). Next, we need to beat our 1 egg white with a tablespoon of sugar until stiff peaks form (you can add a tiny pinch of citric acid). Then add cocoa and 20 grams of nuts to the beaten egg white.
Now we need to spread this egg white mixture along the length between the rolls.
Place our cookies in the oven and bake at 170 degrees for 10 minutes, then reduce the temperature to 160 degrees and bake for another 20 minutes until done. (I want to mention that my jam leaked a bit at the edges).
Remove the finished cookies and let them cool down well. Then cut them into strips about 3 cm wide.
Pour yourself some tea and try it. The cookies turned out very tasty.
Enjoy your meal!