It is common to find peppered smoked mackerel, and tasty it is too. So that serves to inform that mackerel and pepper are a pairing that combine well. Without looking much further it easy to find a multitude of recipes pairing mackerel with horseradish - another peppery character!
This recipe is very much inspired by one for venison in "Rick Stein's Food Heroes - Another Helping". As the idea developed it became increasingly clear that this was a plate that had to work. And it does. Mackerel and horseradish, beetroot and horseradish, peppery horseradish, peppery watercress - no brainer! And the touch of vinegar to cut through the oily mackerel only makes further sense.
On a trip to Athens, being a foodie, I attended a cooking class in an interest to learn more about the true background of Greek cuisine. The class was delivered by Maria Sotou, an enthusiastic and engaging cook, in her charming "Klimataria" taverna. Amongst the many things I learnt, a secret she shared with me and my classmates was that she liked to mix green peppercorns in with black in her peppermill. It's a subtle yet fragrant result. Being that foodie, a couple of days later, I did a "food walk", visiting the markets, shops, cafes and restaurants of Athens where more culinary history and tradition was there for the learning. I bought some green peppercorns in a spice shop and brought them home. Truth be told, I don't think they were the best, but my enthusiasm for a mixture of peppercorns in a pepper-themed dish remains very much intact.
Although this recipe originated from one in which only black peppercorns were used, I have always made that recipe using a mixture of black and white. Here I suggest a more extensive blend.
Peppered Mackerel with Beetroot
Ingredients (serves 2)
4 mackerel fillets, pin bones removed
2 tbsp peppercorns (one or any combination of black, white, pink, green, see note)
Olive oil, for frying
1 small beetroot, cooked and cut into 1cm dice
2 tsp good quality horseradish sauce
2 tsp crème fraiche (or double cream)
Cider or red wine vinegar
Caster sugar, a pinch
Watercress, 2 handfuls (rocket is a very appropriate alternative)
Extra virgin olive oil
Squeeze of lemon juice
Sea salt, to taste
Method
Coarsely crush the peppercorns using a pestle and mortar, then put in a sieve set over a bowl to separate the crushed peppercorns from the powder. Spread the coarsely-crushed peppercorns on a plate.
Season the mackerel fillets with salt on both sides then press them flesh-side-down into the peppercorns to coat.
In a small saucepan, heat the horseradish sauce, crème fraiche, ½ tsp vinegar, pinch of caster sugar, salt to taste and a little of the pepper powder but do not allow to boil. Add the diced, cooked beetroot and warm in the horseradish sauce. Adjust the seasoning for salt, pepper, sugar and vinegar and keep warm.
Dress the watercress with salt, some of the pepper powder, vinegar and extra virgin olive oil.
Heat a little olive oil in a frying pan then fry the mackerel fillets skin-side-down for 1 minute, then turn over and fry for a further minute. Drizzle with a touch of lemon juice.
Arrange 2 mackerel fillets per serving on a plate with half of the beetroot and horseradish and half of the dressed watercress.
Notes
You can, of course, buy different-coloured peppercorns individually. However, a very workable blend is offered by Bart: https://market.bart-ingredients.co.uk/collections/pepper/products/bristol-5-peppercorns-large
Links
"Athens Cooking Lesson & Dinner", Athens Walking Tours, accessed 17 July 2019: https://www.athenswalkingtours.gr/athens-tours/18-athens-cooking-lesson-dinner.html
"Klimataria Tavern cooking class", TripAdvisor, accessed 17 July 2019: https://www.tripadvisor.co.uk/ShowUserReviews-g189400-d3602683-r169983144-Athens_Cooking_Day_Tours-Athens_Attica.html
"Athens Food Tour", Athens Walking Tours, accessed 17 July 2019: https://www.athenswalkingtours.gr/athens-tours/17-sat-6-athens-food-tour.html
References
"Rick Stein's Food Heroes - Another Helping", Rick Stein (2004), pp. 151 https://www.amazon.co.uk/Rick-Steins-Food-Heroes-Another/dp/0563487526