Activate the yeast by dissolving it in warm water. Gradually add flour and salt, kneading until soft and elastic. Divide into 8 portions, cover, and let rest for about 25 minutes.

Prepare the filling by boiling the potatoes until tender. Drain and mash, then mix with cheddar cheese, additional salt, and black pepper.

Roll out each dough portion, spreading a layer of softened butter on each sheet, stacking them, and freeze for about 30 minutes.

After freezing, roll the dough into a square, cut into smaller squares, and add a spoonful of potato mixture in the center. Seal edges carefully.

Preheat the oven to 190°C (375°F). Arrange pastries on a baking tray lined with parchment paper and brush tops with beaten egg yolk.

Bake for 20-25 minutes, until cookies are golden brown. Allow to cool slightly before serving.