01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - Heat olive oil in a skillet over medium heat. Cook the onion for 2 minutes, then add garlic and sauté until fragrant.
03 - Add fresh spinach to the skillet and cook until wilted, or add thawed, drained spinach and heat through. Allow to cool, then squeeze out excess liquid and chop coarsely.
04 - In a mixing bowl, combine prepared spinach, feta, ricotta, sautéed onion and garlic, dill, parsley, whole egg, lemon zest, nutmeg, salt, and pepper. Stir until thoroughly combined.
05 - Unroll puff pastry on a lightly floured surface. With the longer edge facing you, spread the filling evenly along the edge, leaving a 3/4-inch border.
06 - Carefully roll pastry, enclosing the filling tightly in a log. Pinch the seam to seal.
07 - Gently shape the filled log into a spiral. Transfer to the prepared baking sheet.
08 - Brush the spiral with beaten egg yolk. Sprinkle with sesame or nigella seeds as desired.
09 - Bake for 30 to 35 minutes until golden and crisp.
10 - Allow to cool slightly before slicing. Serve warm or at room temperature.