Preheat oven to 375°F (190°C) and line a baking sheet with parchment paper.
Heat olive oil in a skillet over medium heat. Sauté the diced onion until soft and translucent.
Add minced garlic and cook for 30–60 seconds until fragrant.
Stir in the chopped spinach and cook until wilted. If using frozen spinach, ensure it is well drained and warmed through.
Remove the skillet from heat and let the spinach mixture cool slightly.
In a mixing bowl combine the cooled spinach mixture with crumbled feta, beaten egg, chopped dill, black pepper, and salt if needed. Mix until well combined.
Carefully unroll filo dough and keep covered with a damp towel to prevent drying.
Brush a sheet of filo with melted butter, place another sheet on top and brush again. Cut the layered filo into rectangles sized for individual crisps.
Place a spoonful of the spinach-feta filling onto each filo rectangle and fold or shape into parcels, triangles, or cups as desired. Seal edges with a little butter.
Arrange the filled crisps on the prepared baking sheet and brush the tops lightly with additional melted butter.
Bake for 12–15 minutes, or until the filo is golden brown and crisp.
Remove from oven, let cool slightly on the baking sheet, then transfer to a wire rack. Serve warm or at room temperature.
