Preheat the oven to 180C/350F/Gas 4.
For the soup, heat the oil in a small saucepan, add the onion and leek and sauté for three minutes. Add the garlic and fry for one minute. Add the peas and stock and simmer gently for five minutes. Season to taste with salt and freshly ground black pepper.
For the croutons, place the oil and cayenne pepper into a bowl, add the torn bread, season to taste with salt and freshly ground black pepper. Mix to coat.
Place the pieces of bread onto a baking sheet and bake in the oven for eight minutes or until crisp and golden.
To serve, spoon the soup into a bowl, top with the croutons and garnish with roughly chopped mint leaves.