Preheat the oven to 200°C. Grease a silicone or 12-hole muffin tin with 3 Tbsp (45 ml) softened butter, place on a baking tray and set aside.
Add 2 Tbsp (30 ml) olive oil to a medium, non-stick frying pan over high heat. Add the onion and fry for 1-2 minutes to soften. Add the red pepper and tomato halves and continue to cook for a further 5 minutes until softened, stirring every few minutes.
Add the sliced mushrooms and cook for a further 5 minutes. Season with salt and pepper to taste. Remove from the heat and stir in the basil.
For the egg custard, in a medium bowl, combine the eggs, milk / or Maas/ or yoghurt, season with salt and pepper and add the grated cheddar cheese. Whisk well to combine.
Add the cooked vegetables to the egg custard, whisk well and divide the egg mixture between the muffin tin.
Place the muffin tin into the oven to bake for 25-30 minutes, or until the egg mixture is set and golden on top.
Remove from the oven and allow to cool in the tin before unmoulding.
