Mackerel, in order to be truly delicious, must be spankingly fresh and served very hot, straight from the oven or barbecue. Beetroot and horseradish are its perfect partners. Here, the beetroot is sliced paper-thin and raw; eaten this way, its flavour is sweet and earthy. The freshly grated horseradish lends heat and is a lovely foil for the mackerel's oily flesh.
You should be able to find fresh horseradish root at good greengrocers. Better still, it is easy to grow or forage – here at Petersham we are lucky enough to have plenty close by.
The fish in this photograph, right, is quite hefty – 290g to be precise – but setting aside the head and bones, what is left is the perfect amount of flesh.
1 medium-sized or 2 smaller mackerels per person
One horseradish root, rinsed, peeled and grated on the finest side of your grater
120ml/4fl oz crème fraîche
1 tsp of Dijon mustard
300g/10oz well-rinsed young spinach leaves
4 beetroot – red, yellow, striped or a combination of all three
1 tbsp aged balsamic vinegar
60ml/2fl oz olive oil
Salt and freshly ground black pepper
Ask your fishmonger to gut and scale the mackerel. Just before cooking, rinse well to remove any blood that may be lingering in the cavity. Preheat the grill to its highest possible setting.
Place the horseradish, Dijon mustard and crème fraîche into a bowl and stir well to combine. Season with a little salt but no pepper, and set aside. Take the well-rinsed spinach and put into a pan while still damp. Heat gently until just soft.
Wash the beetroot very well, using a scrubbing brush if possible, and slice into fine rounds. Toss together with the olive oil and balsamic vinegar, and season.
Slash the mackerel three times on both sides – this will help it to cook evenly and season both inside and out. Lay under your grill and cook for 4 minutes on each side. Serve the mackerel straight away with the beetroot and spinach divided between each fish, and the horseradish cream alongside.