There’s a supposedly unbreakable rule in Italian cooking that says you are never meant to mix seafood and parmesan although like many of these things it appears to be entirely arbitrary; I read an article about this by Heston Blumenthal years ago but only recently did I look more closely behind the science of why the two are actually a very good combination. The main reason is due to the compounds present in parmesan (glutamate) and fish (inosinate): when these two combine they have a synergistic effect and this increases the perception of umami by a factor of eight.
After discovering mackerel has some of the highest concentrations of inosinate of any fish I got the idea for adding a parmesan crust as a way of combining the two ingredients. This is one of the few times I would recommend using a non-stick pan because it really helps here as the cheese often sticks to the surface when browning and this can make it difficult to flip the fish.
There is also a third compound called guanylate which enhances the umami synergy even more and is very prevalent in mushrooms (especially when dried) so I decided to add some of those too. The process of drying increases the amount of guanylate significantly but I didn’t think the texture would be appropriate and instead I chose to slow roast fresh portobellos at a low temperature in the oven to cook them and partially dry them out as well.
Finally, a word of warning about horseradish is that its pungent flavour is dissipated by heat: make sure to add it to the sauce just before you serve for maximum impact.
For the mackerel
1 egg lightly beaten
2 mackerel fillets
15ml rapeseed oil
For the sauce
200ml creme fraiche
100ml chicken stock
100g of peas
15g freshly grated horseradish
For the mushrooms
25ml olive oil
2 large portobello mushrooms
- For the mushrooms, preheat the oven to 100°C.
- Season the mushrooms generously, pour over the olive oil and cook for 6 hours.
- For the sauce, cook the peas in the stock with a pinch of sugar and salt.
- When cooked, remove the peas and reserve the cooking liquid.
- Place the the creme fraiche and the stock in a pan and reduce by a third.
- Add the peas to heat them through and just before serving season to taste and add the horseradish.
- For the mackerel, mix the breadcrumbs and the parmesan together thoroughly.
- Coat the skin side of one of the fillets in flour, shaking off any excess.
- Dip the floured side of the fish into the beaten egg and then dip the same side into the breadcrumb mixture whilst ensuring there’s an even coating over the skin.
- Repeat for the other mackerel fillet.
- Place a pan on a medium heat to warm up and then add the oil.
- Place the fillets skin side down in the pan for around two minutes or until the coating has browned.
- Season the uncoated side of the fish lightly with salt and after taking the pan off the heat turn the fillets over.
- To plate, cut the mushroom in to large slices and place in the middle, lay the mackerel skin side up on the mushrooms and top with the horseradish sauce.