1. Thinly slice the onions. Sauté the onions in oil for 3-4 minutes until they are clear.
2. Whisk the eggs slightly. Season to taste with salt, pepper and thyme, then add to the pan.
3. Cook for a couple of minutes until the egg begins to set, then add slices of Castello Extra Creamy Brie with Chilli and bresaola. Bake at 180°C until firm, approximately 10 minutes.
4. Serve the frittata hot or warm and with a lovely green salad.