Heat the olive oil in a large pot over medium heat. Add the onion, celery, garlic, anchovy and chilli, season with salt and pepper and cook for 5 minutes or until soft.
Boil the potato until knife tender. Drain, let cool, cut into thick slices and set aside.
Add the tomato, wine and stock and cook for 15 minutes on medium-high heat. Break the tomatoes up with a flat spoon. Add the prawns, potatoes, lemon zest and juice and capers and cook for 5 minutes or when the prawns turn pink.
Serve with the toasted crostini rubbed with the extra garlic clove and a small spoonful of the garlic mayonnaise.