Savoury custard with mackerel and pickled rhubarb (chawanmushi)

Method

1. To pickle the rhubarb, put the vinegar, sugar, salt and 100ml water in a small saucepan. Heat until the sugar dissolves, then simmer for 2 minutes. Put the rhubarb and ginger in a clean heatproof container, then pour over the pickling liquid and cover. Chill for at least 1 hour.
2. Put 4 deep ramekins, cups or bowls (that hold at least 200ml) in a saucepan wide enough so they fit in with some space between each. Pour enough water in the saucepan to reach halfway up the sides.
3. In a bowl, whisk together the eggs, dashi, mirin, soy and salt until well combined. Pass through a fine sieve into a jug (this helps achieve a silky texture).
4. Take the ramekins out of the saucepan and bring the pan of water to the boil. Divide the mushrooms, mackerel and spring onions between the ramekins then pour over the custard mixture. Cover each ramekin with a lid or foil. Once the water has come to the boil, reduce the heat to very low and carefully lower in the ramekins. Cover and cook very gently (you don’t want the water to boil) for 15-20 minutes until the custard has set. Test the custard by tilting a cup slightly – if it is runny, keep going.
5. Carefully remove the custard ramekins/cups from the water and serve with the pickled rhubarb on top.