In a medium size saucepan, heat 2 tablespoons of oil and fry the onion for 5 minutes. Stir occasionally.
Add in the beans with the stock and continue to cook for a further 5 minutes until the beans are soft. Allow to cool slightly.
To make the black olive relish, place the olives, parsley and anchovies in a bowl. Pour over the remaining tablespoon of oil and the lemon juice. Season with salt and pepper and stir well.
Place the beans with their liquid in a food processor with 1 tbsp of oil and the remaining lemon juice. Season with salt and pepper and blitz to a smooth puree.
Place the bread on a hot griddle pan and cook for 2 minutes on each side until lightly charred on both sides.
To serve, spread some of the cannellini puree on top of each warm bruschetta and spoon on a little olive relish. Drizzle with a touch more extra virgin on top and place on a large serving plate. Perfect with a good cold glass of Prosecco.