Preheat the Oven: Preheat your oven to 375°F (190°C).

Sauté Aromatics: In a large skillet, heat the olive oil over medium heat. Add the chopped onion and garlic, sauté until softened, about 5 minutes.

Add Spinach: Stir in the chopped spinach and cook until wilted (if using fresh) or heated through (if using frozen). Remove from heat and let cool slightly.

Mix Filling: In a mixing bowl, combine the cooked spinach mixture, crumbled feta cheese, dill, and beaten eggs. Season with salt and pepper to taste.

Assemble Spanakopita: Lay one sheet of phyllo dough on a clean surface and brush lightly with melted butter. Place another sheet on top and brush again. Repeat with 3-4 layers. Spoon some of the filling along one edge and fold the phyllo over to encase the filling. Roll into a log or coil shape, tucking in the ends. Repeat until all the filling is used.

Bake: Place the rolled spanakopita on a baking sheet lined with parchment paper. Brush the tops with remaining melted butter. Bake for 30-35 minutes, or until golden brown and crispy.

Serve: Let cool slightly before slicing into pieces. Serve warm or at room temperature.