Prepare the Filling

Cook the spinach: Heat the olive oil in a large skillet over medium heat. Add the chopped onion and cook until translucent, about 5 minutes. Add the garlic and cook for another minute. Add the spinach and cook until wilted and most of the liquid has evaporated, about 5-7 minutes. Remove from heat and let cool.

Mix the filling: In a large bowl, combine the cooked spinach mixture, crumbled feta cheese, fresh dill, parsley, beaten eggs, ground nutmeg, salt, and pepper. Mix well to combine.

Assemble the Pastries

Prepare the phyllo dough: Preheat the oven to 375°F (190°C). Line two baking sheets with parchment paper. Unroll the phyllo dough and cover it with a damp cloth to prevent it from drying out. Take one sheet of phyllo dough and place it on a clean work surface. Brush lightly with melted butter. Place another sheet on top and brush with more butter. Repeat until you have a stack of 3 sheets.

Cut and fill: Using a sharp knife or a pizza cutter, cut the layered phyllo sheets into strips about 3 inches wide. Place a tablespoon of the spinach and feta filling at the bottom of each strip. Fold one corner of the strip over the filling to form a triangle. Continue folding the triangle along the strip, maintaining the triangular shape, until you reach the end. Brush the outside of the triangle with more melted butter. Repeat with the remaining phyllo sheets and filling.

Bake the Pastries

Bake: Place the triangles on the prepared baking sheets, seam side down. Bake in the preheated oven for 20-25 minutes, or until the pastries are golden brown and crispy. Rotate the baking sheets halfway through the baking time to ensure even browning.

Serve: Let the pastries cool slightly before serving. Enjoy them warm or at room temperature.