Preheat your oven to 375°F (190°C) and grease a round baking pan or cast-iron skillet with a little olive oil.

In a large mixing bowl, combine the crumbled feta, ricotta cheese, and 2 of the eggs. Mix well.

Add the dried spinach and black pepper to the cheese mixture and stir until evenly distributed.

In a separate small bowl, whisk together the olive oil, sparkling water, and the remaining egg. This mixture helps keep the phyllo flaky and moist.

Lay out one sheet of phyllo dough on a clean surface. Lightly brush it with the oil-water mixture. Place a second sheet on top and brush again.

Spoon a thin line of the spinach and cheese filling along the long edge of the layered phyllo sheets.

Roll the dough up tightly into a long log or 'snake', enclosing the filling completely.

Coil the rolled log into a tight spiral shape and place it in the center of your prepared baking pan.

Repeat the layering, filling, and rolling process with the remaining ingredients. Place each new log at the end of the previous one in the pan, continuing the spiral outward until the pan is full.

Brush the top of the entire pastry with any remaining liquid mixture and sprinkle with sesame seeds.

Bake for 35 to 40 minutes, or until the burek is deep golden brown and crispy. Let cool for 10 minutes before slicing into wedges.