Cannellini bean and leek soup with chilli oil

Name: Cannellini bean and leek soup with chilli oil
Prep time: 10 min
Total time: 10 min
Cuisine: European, British
Ingredients: 4 medium leeks, trimmed (white and pale green part only); 1 tablespoon olive oil; 15g butter (Optional); A few sprigs of thyme, leaves only, roughly chopped; 1 bay leaf; 3 garlic cloves, finely chopped; 1.3 litres vegetable stock; 2 x 400g tins cannellini beans, drained and rinsed; A handful of oregano, roughly chopped; A bunch of parsley, roughly chopped; Sea salt and freshly ground black pepper; For the chilli oil; 4 red chillies, deseeded and sliced; 200ml olive oil; A few sprigs of thyme, leaves only; 1 garlic clove (unpeeled), bashed