Shred the cheese using a food processor and place in a large bowl.
Add the diced onion, chopped parsley, black pepper, Aleppo pepper (if using), and 2 of the eggs to the cheese. Mix until fully combined.
Lay one half-sheet of phyllo dough on your work surface and brush lightly with melted butter. Top with a second half-sheet and brush lightly with butter again.
Place 1½ to 2 tablespoons of the cheese filling near the top of the phyllo strip.
Fold into a triangle shape, continuing to fold flag-style down the length of the strip.
Brush the final flap with butter and press to seal.
Repeat with remaining phyllo and filling, arranging triangles on a baking sheet, spaced apart.
Whisk the remaining egg with a splash of water and brush lightly over each triangle.
Sprinkle very lightly with sea salt flakes.
Bake at 375°F for 15–17 minutes, until golden and puffed.