Preheat the oven to 200°C / fan 180°C / gas 6. Put the leeks in a medium roasting tray, drizzle over half of the oil, add the garlic and rosemary and shake to combine. Season with freshly ground black pepper and pour over the wine and stock. Roast for 30 minutes, turning occasionally until the leeks are tender and the liquid has cooked off.
Meanwhile, dry fry the bacon over a medium heat for 3-4 minutes until crisp then remove from the pan and set aside. Add the remaining oil and the bread to the pan and return to the heat. Cook, stirring, until crisp.
To serve, transfer the roasted vegetables to a warm serving dish and scatter over the bacon and toasted croutons.