If using, heat a griddle pan until it's very hot. Drizzle or spray bread with a little olive oil, then grill on both sides until toasted and marked. Once toasted, rub the surface with the cut garlic clove.
While the bread is grilling, roughly mash the cannellini beans. I like them about half mashed with some whole beans still in the mix. Reserve a few capers for garnish, finely chop the rest and add them to the beans, along with the cherry tomatoes and basil leaves. Drizzle in a little olive oil (1-2 tsp), add a good grind of salt and pepper, then stir to combine the mixture. Pile it onto the grilled sourdough and drizzle with a little more olive oil, and balsamic vinegar.