Prepare the dough: In a large mixing bowl, combine the 300g (2.5 cups) of all-purpose flour and 5g (1 tsp) of salt. Make a well in the center.

Add the 150ml (0.6 cups) of warm water, 1 large egg yolk, and 30g (2 tbsp) of melted butter to the well in the flour. Gradually incorporate the flour from the sides into the wet ingredients, mixing with a fork or your hands until a shaggy dough forms.

Turn the dough out onto a lightly floured surface. Knead for about 8-10 minutes until the dough is smooth, elastic, and no longer sticky. If it's too sticky, add a tablespoon of flour at a time. If too dry, add a teaspoon of water.

Shape the dough into a ball, place it back into the bowl, cover with a damp cloth or plastic wrap, and let it rest at room temperature for at least 30 minutes. This allows the gluten to relax, making it easier to roll out.

Prepare the filling: While the dough rests, combine 500g (2 cups) of cottage cheese, 30g (0.25 cup) of finely chopped fresh tarragon, 1 large egg yolk, 2g (0.5 tsp) of salt, and 1g (0.25 tsp) of black pepper in a medium bowl. Mix thoroughly until well combined.

Preheat a large pot or Dutch oven with at least 4 liters (1 gallon) of water and 10g (2 tsp) of salt over medium-high heat. Bring to a rolling boil.

On a well-floured surface, roll out the rested dough into a large, thin rectangle, approximately 40cm x 30cm (16 x 12 inches) and about 2mm (less than 1/8 inch) thick.

Spread the cottage cheese and tarragon filling evenly over the rolled-out dough, leaving a 2.5cm (1 inch) border along the edges.

Carefully roll up the dough tightly, starting from one of the longer sides, like a jelly roll. Pinch the seam and the ends firmly to seal the filling inside.

Using a sharp knife dusted with flour, cut the rolled log into individual štruklji, each about 4-5cm (1.5-2 inches) wide.

Gently place the cut štruklji into the boiling water, ensuring not to overcrowd the pot. Cook in batches if necessary. Do not boil vigorously; maintain a gentle simmer.

Simmer the štruklji for about 10-15 minutes, or until they float to the surface and are cooked through. They should be slightly puffed and tender.

While the štruklji are cooking, melt 50g (4 tbsp) of unsalted butter in a small skillet over medium heat. If using breadcrumbs, add them to the melted butter and toast until golden brown and fragrant, stirring constantly.

Using a slotted spoon or spider strainer, carefully remove the cooked štruklji from the boiling water and drain them well. Place them on a serving platter.

Drizzle the toasted buttered breadcrumbs (if using) over the hot štruklji. Alternatively, simply drizzle with melted butter. Serve immediately.

Optional: Serve with a dollop of sour cream or plain yogurt on the side.