Warm the oil in a large saucepan over a medium heat. Add the onion then cook and stir until soft, about 4 to 6 minutes. Add the nuts, sprouts and pour in the stock. Increase the heat and bring to the boil, reduce the heat and simmer for 15 minutes.
Meanwhile, heat a small frying pan and add the salami. Stir occasionally until crispy, then remove from pan and set aside. Add the rendered fat to the saucepan with the other ingredients and stir.
Divide the soup between two warmed bowls and top with the crispy salami. Serve immediately.
If you prefer a smoother soup, use a handheld immersion blender at the end of step 2.