We picked up the recipe for this starter, from a chatty waiter in Albufeira, Portugal, although it appears that the recipe originates in northern Portugal, rather than The Algarve.
1 sliced onion
1 large tomato, skinned and roughly chopped
olive oil and butter
salt and pepper
Cook onion and tomato together, until tender. Season to taste. Add sprinkling of fresh chopped basil. Meanwhile, butter two cocottes or ramekins. Crack an egg carefully into each one (it needs to be whole). Bake in the oven, until the whites are set. Remove from dishes and serve on the tomato-onion mixture.