Finely chop the onion. Cut the unpeeled potatoes into 2cm chunks. Drain and rinse the beans. Crumble the stock cubes into a heatproof jug, add 750ml (3 cups) boiling water and stir to dissolve.
Step 2 — Cook onion
Heat 1 tsp olive oil in a large saucepan over medium heat. Cook the onion, stirring regularly, for 3-4 mins until softened. Add the Italian seasoning and stir for 30 secs or until fragrant.
Step 3 — Cook soup
Add the potato, beans, stock, tomatoes and 2 tsp sugar to the onion and stir to combine. Season with salt and pepper and bring to a simmer. Reduce the heat to medium-low and cook, covered, for 15-20 mins until the potato is very tender.
Step 4 — Make dressing
Meanwhile, preheat the grill to high. Finely chop the olives, capers and parsley leaves, discarding the parsley stems. Combine 1½ tbs extra virgin olive oil and 2 tsp white wine vinegar in a bowl. Add the olives, capers and parsley and stir to combine. Season with pepper.
Step 5 — Toast croutons
Line an oven tray with foil. Coarsely tear the wholemeal rolls into bite-sized chunks and put on the lined tray. Drizzle with 1 tsp olive oil, season with salt and pepper and toss to coat. Grill the croutons, tossing occasionally, for 3-5 mins until golden and toasted.
Step 6 — Get ready to serve
Lightly crush some of the beans and potato in the soup with a potato masher. Taste, then season with salt and pepper. Divide the soup among bowls. Scatter with the croutons and drizzle with the olive caper dressing to serve.