The beef for this broth is flavoured with a deeply umami seaweed butter. You will need to soak the dried kombu and dried mushrooms overnight for the broth.
For the broth
- 1 postcard-sized piece dried kombu
- 12 dried shiitake mushrooms
- 1 garlic clove, peeled and smashed
- 1 knob fresh ginger, peeled and finely chopped
- 4 tbsp soy sauce
- 4 tbsp mirin
- 2 tsp caster sugar
For the butter
- 150g/5½oz salted butter
- 3 anchovy fillets, chopped
- 2 tbsp chopped curly leaf parsley
- 2 tbsp chopped fresh or rehydrated mixed coloured seaweed (see Recipe Tip)
For the beef
- dash oil
- 2 x 300g/10½oz beef fillet steaks
- 100g/3½oz mixed oriental mushrooms, cleaned
- 2 tbsp baby or micro watercress leaves, to garnish
- 1 tbsp fresh or rehydrated mixed coloured seaweed, to garnish (see Recipe Tip)
To make the broth, heat 400ml/14fl oz of water and add the kombu and mushrooms. Leave overnight. Strain the liquid into a clean bowl through a sieve lined with muslin and discard the kombu and mushrooms.
To make the butter, mix all the butter ingredients together in a bowl, roll into a tube shape, wrap in cling film and place in the fridge.
To continue the broth, pour the liquid into a clean pan, bring to a simmer and add the garlic, ginger, soy sauce, mirin, caster sugar and 600ml/20fl oz of water. Add salt to taste. Keep warm.
To make the beef, heat a frying pan until very hot. Add a dash of oil and sear the beef until coloured all over. The beef should still be very rare inside.
Rest the beef in a warm place, topped with a couple of slices of the butter. The remainder of the butter can be saved in the fridge and used in another recipe.
Add the mushrooms and seaweed garnish to the hot broth. Cut the beef fillet into long diagonal slices and transfer to two bowls. Top with the broth and garnish with the watercress. Serve.
To rehydrate the seaweed, soak in a bowl of cold water according to packet instructions (normally 5–10 minutes) and then chop in preparation for the recipe.