Step 1: Prepare the Oven and Pan : Preheat your oven to 375°F (190°C). Lightly grease a 12-cup muffin tin with butter or non-stick spray.
Step 2: Prepare the Crust : Roll out the pie crust on a lightly floured surface. Using a round cookie cutter (about 3 inches in diameter), cut out 12 circles. Press each circle gently into the muffin tin cups to form a small crust base.
Step 3: Make the Filling : In a medium bowl, whisk together the eggs, milk, salt, pepper, and nutmeg until smooth. Stir in the cooked spinach, crumbled feta, and chopped onion (if using).
Step 4: Assemble the Mini Quiches : Spoon about 2 tablespoons of filling mixture into each crust cup, filling them about ¾ full. Ensure the filling is evenly distributed among all cups.
Step 5: Bake the Quiches : Place the muffin tin in the preheated oven and bake for 20–25 minutes, or until the tops are golden and the centers are set. Remove from the oven and let them cool for 5 minutes before gently lifting them out.