Making soup in the oven

This is currently one of my favourite things to have when I'm home alone at lunchtime!

-One tin of cannelini or borlotti beans (borlottis have more of their own flavour, cannelinis go mushy which helps the texture)
-One onion, four medium garlic cloves (or both)
-Olive oil - more than you think you'll need
-Two teaspoons of yeast extract dissolved in a coffee mug of hot water (just off the boil is best)

Tip the beans into a roasting tray. Add the chopped onion and/or crushed garlic and stir it in. Cover everything with olive oil and put in a hot-ish oven (200C or thereabouts). Take out after 20 mins or so and add the yeast extract liquid. Put back in the oven for another 20-odd mins. Take out and eat.