Preheat the oven to 350 degrees F. Mold 3 filo squares into the bottom of a miniature (1-inch) muffin tin. Place 3 more filo squares at a 45 degree angle on top and press gently into the muffin cups. Brush lightly with melted butter. Cook until lightly golden brown, 4 to 6 minutes. Let cool. Place on a baking sheet and cover tightly with plastic wrap until ready to use. Heat the oil in a medium nonstick skillet over medium heat. Add the onions and garlic. Season with 1/4 teaspoon of the kosher salt and 1/8 teaspoon of the pepper. Cook until the onions are tender, 5 to 7 minutes. Add the lamb, black currants, cumin, ginger, cinnamon, allspice, remaining 1/4 teaspoon kosher salt, and remaining 1/8 teaspoon pepper. Cook until the lamb is cooked through, about 5 minutes. Stir in the mint. To Assemble: Place 1 heaping teaspoon of the lamb mixture in each filo cup. Top with a heaping 1/4 teaspoon feta. Serve while filling is warm.
The filo cups can be prepared up to 5 days in advance and stored in an airtight container. The filling can be prepared up to 2 days in advance and refrigerated. (Do not add the mint until assembly.) The cups can be filled up to 1 hour in advance and warmed in a 300 degree F. oven for 5 minutes.
Recipe from Cocktail Food by Mary Corpening Barber and Sara Corpening Whiteford, published by Chronicle Books