01 -
Preheat oven to 200°C (400°F) to ensure proper baking temperature.
02 -
Lightly grease a 25cm (10-inch) quiche or tart pan with vegetable oil or cooking spray to prevent sticking.
03 -
Heat a medium frying pan over medium-high heat with a light coating of oil. Cook diced onion until translucent, about 5 minutes. Add spinach and cook until just wilted, 2-3 minutes. Remove from heat and set aside to cool slightly.
04 -
In a large bowl, whisk together eggs, egg substitute, flour, and baking powder until well combined. Gradually incorporate the milk, whisking until smooth. Season with a pinch of cayenne pepper.
05 -
Fold the cooled spinach-onion mixture into the egg mixture, ensuring even distribution of vegetables.
06 -
Pour the mixture into the prepared pan, distributing the vegetables evenly. Sprinkle crumbled feta cheese over the top.
07 -
Bake in preheated oven for 25 minutes, or until the center is set and edges are golden brown. Test for doneness by inserting a toothpick into the center - it should come out clean.
08 -
Allow quiche to rest for 5 minutes before slicing. Serve warm or at room temperature, optionally with a side salad.