Step by step recipe:

1. 7 min.

   Prepare the tomatoes

   
   Peel 4 tomatoes (choose fairly large ones). Slice off the top and scoop the flesh and seeds out of each tomato. You should end up with hollow tomatoes that will be able to hold the eggs.
2. 30 min.
   Sprinkle the insides of the tomatoes with fine salt and stand them upside down on a wire rack.
   
   Leave for at least 30 minutes for some of the juices to drain off.
3. 1 min.
   Coat the outside of the tomatoes with olive oil, using a brush, then salt them.
4. 2 min.

   Fill the tomatoes

   
   Preheat the oven to 390°F (200°C).
   
   Sit each tomato in a ramekin (to stop them splitting during cooking), then put a teaspoonful of caramelized onions in the bottom of each one.
5. 2 min.
   Pour an egg white into each tomato. Keep the yolks separate.
6. 20 min.

   Cook the egg whites

   
   Bake the egg whites in the tomatoes for about 20 minutes until set.
7. 1 min.

   Cook the egg yolks

   
   Gently place an egg yolk onto the top of each tomato, salt and pepper, then return to the oven for 1 minute - just enough to heat the yolk through, not cook it (this is important).
8. 
   Serve immediately.