This can be stored for 2 days. The crust will harden slightly.
I browned my onions a little bit in oil in a pan before using.This is optional.
Other options of topping - garlic , cheese, tomatoes ,dried or fresh herbs ,pepper , salt , sliced vegetables, meat.
if you have trouble getting the bread out of the pan , let it cool and then gently release the sides and try to slide a knife under.
If you don't want to use a square pan, you can spread the dough on a parchment lined baking sheet and follow the rest of the recipe for a more rustic looking focaccia.