Start by preheating your oven to 200°C (392°F) and lightly greasing your muffin tin or tart pans. In a frying pan over medium heat, warm the olive oil and sauté the chopped onion for about 3–4 minutes until it softens and turns slightly golden. Add the minced garlic and cook for another 30 seconds until fragrant. Then, stir in the fresh spinach and cook until wilted. If you’re using frozen spinach, simply add it after the garlic and cook until heated through, making sure to squeeze out excess moisture beforehand.

Once cooked, remove the mixture from the heat and let it cool slightly. In a separate bowl, whisk the eggs with the crème fraîche, a pinch of salt, pepper, and optional herbs. Stir in the crumbled feta and the cooled spinach mixture, combining everything until evenly mixed.

Next, unroll your puff pastry and cut it into squares large enough to line the bottom and sides of each muffin cup or tart tin. Press the pastry squares gently into each cavity, allowing the corners to come slightly above the edge. Spoon the spinach and feta mixture into each one, filling them nearly to the top.

Bake in the preheated oven for 18–20 minutes or until the pastry is golden brown and the filling is set. Let the tarts cool slightly before removing them from the tin. They can be served warm, at room temperature, or chilled depending on your preference.