Prepare a broth from the shrimp heads, onion and wild garlic. Sauté some spring and dry onions together with the wild garlic and add the broth and tomato. Add the tarhana, stirring continuously. Fry sourdough bread cubes in plenty of olive oil. Serve the tarhana with basil, the fried bread cubes and the feta cheese, drizzling some extra virgin olive oil on top.