Prepare the dough: In a large bowl, combine 500g (4 cups) of all-purpose flour with 1 tsp (5g) of salt. Make a well in the center. Add 150ml (5 fl oz) of lukewarm water, 1 large egg (approx. 50g), and 125g (4.4 oz or 1/2 cup + 1 tbsp) of softened unsalted butter. Mix with your hands or a stand mixer until a cohesive dough forms. Knead on a lightly floured surface for about 8-10 minutes until smooth and elastic. Cover the dough with plastic wrap or a damp cloth and let it rest at room temperature for at least 30 minutes.

Prepare the poppy seed filling: In a saucepan, combine 200g (2 cups) of ground poppy seeds with 100g (1/2 cup) of granulated sugar and 250ml (1 cup) of whole milk. Cook over medium heat, stirring constantly, until the mixture thickens, about 5-7 minutes. Remove from heat, stir in 1 large egg (approx. 50g), and let it cool completely. If the mixture is too thick, you can add a splash more milk.

Prepare the apple filling: Peel, core, and thinly slice 1kg (2.2 lb) of tart apples. In a large bowl, toss the apple slices with 100g (1/2 cup) of granulated sugar, 2 tsp (4g) of ground cinnamon, 1 tsp (2g) of lemon zest, and 50g (1/2 cup) of plain breadcrumbs. The breadcrumbs will absorb excess moisture from the apples.

Prepare the cottage cheese filling: In a medium bowl, combine 500g (2 cups) of full-fat cottage cheese, 200g (7 oz) of full-fat sour cream, 1 tsp (5ml) of vanilla extract, and 2 egg yolks (approx. 40g). Mix well until smooth and creamy. Ensure the cottage cheese is well-drained if it seems very wet.

Divide the dough: After resting, divide the dough into 9 equal portions. Roll each portion into a ball. Keep them covered to prevent drying.

Roll out the dough layers: On a lightly floured surface, take one portion of dough and roll it out as thinly as possible into a rectangle, approximately 30cm x 20cm (12 x 8 inches). The dough should be almost translucent. Carefully transfer this layer to a baking dish (approximately 25cm x 35cm or 10x14 inches) that has been lightly greased or lined with parchment paper. Repeat this process with 4 more portions of dough, layering them in the baking dish. Brush each layer generously with melted unsalted butter (you will use about half of the 250g total butter for this).

Assemble the first filling: Spread the cooled poppy seed mixture evenly over the 4 dough layers in the baking dish.

Roll out and layer the next dough portions: Roll out 2 more portions of dough very thinly, as done before. Place one layer over the poppy seed filling and brush it with melted butter. Place the second layer on top and brush it with melted butter.

Assemble the second filling: Spread the apple mixture evenly over the 2 buttered dough layers.

Roll out and layer the final dough portions: Roll out the remaining 2 portions of dough very thinly. Place one layer over the apple filling and brush with melted butter. Place the final dough layer on top and brush it generously with the remaining melted butter.

Assemble the final filling: Spread the cottage cheese mixture evenly over the top dough layer.

Prepare for baking: Preheat your oven to 180°C (350°F). In a small bowl, whisk the 2 egg whites (approx. 60g) until slightly frothy. Brush the top layer of the gibanica generously with the whisked egg whites. This will help create a beautiful golden crust.

Bake the gibanica: Place the baking dish in the preheated oven. Bake for 45-55 minutes, or until the top is golden brown and puffed up. The pastry should be crisp.

Cool and serve: Remove the gibanica from the oven and let it cool in the baking dish for at least 15-20 minutes before slicing. This allows the layers to set. Cut into squares (approximately 10cm x 12cm or 4x5 inches) and serve warm or at room temperature.