Cook the spinach with a little drizzle of oil until it's wilted. Squeeze out the excess moisture by pressing it in a sieve.
In a frying pan, add the anchovies, garlic, and rosemary in a little oil and cook until the anchovies dissolve.Add the double cream and reduce by half then add the spinach and combine.
Dust the slices of lambs liver with well-seasoned flour and preheat a frying pan on the stove. Add a little oil and the slices of liver and cook for 1 minute on each side.
Toast the sourdough and spoon on the creamy spinach mix then lay the lamb's liver on top.Serve.