Preheat your oven to 375°F (190°C) and grease a standard muffin tin.

In a medium skillet, heat 1 tablespoon of olive oil over medium heat and sauté chopped onion for about 3 minutes.

Add minced garlic and cook for an additional minute until fragrant.

Stir in chopped spinach and cook for 2-3 minutes until wilted.

Remove from heat and allow to cool slightly.

In a large mixing bowl, whisk together eggs, milk, and heavy cream.

Sprinkle in the salt, black pepper, and nutmeg, blending well.

Fold in the grated cheddar and Parmesan cheeses, followed by the cooled spinach and onion mixture.

Brush each filo pastry sheet with melted butter and stack them, cutting into squares.

Press the filo squares into the prepared muffin tin and fill with the spinach and cheese mixture.

Bake for 20-25 minutes until filling is set and tops are golden brown.

Remove from the oven, cool for 5-10 minutes, and serve warm.