Wild fennel is prolific along our coastlines; you can't miss its tall, fern-like leaves and you won't be able to resist foraging for it once you've identified it. Its slightly aniseed-like flavour is the perfect accompaniment to fish and if you gather enough you can chop it and keep it in the freezer for future use.
1 whole sea trout weighing about 2kg, gutted and scaled
For the court bouillon
1 small onion, peeled and roughly chopped
1tsp fennel seeds
1 bay leaf
A few sprigs of thyme
100ml white wine
1tbsp sea salt
For the hollandaise
40ml white wine vinegar
1 small shallot, chopped
The thick stalks from the fennel or 1tsp fennel seeds
3 small egg yolks
200g unsalted butter
Salt and freshly ground white pepper
1tbsp chopped wild fennel
First make the sauce: put the vinegar, water, shallot, peppercorns and fennel stalks in a saucepan and reduce the liquid by boiling for a few minutes until there is no more than a dessertspoonful. Strain through a sieve and leave to cool.
Melt the butter and simmer for 5 minutes. Remove from the heat, leave to cool a little, then pour off the pure butter where it has separated from the milk solids – discard the milk solids. This helps to keep the sauce thick. Put the egg yolks into a small bowl (or double boiler if you have one) with half of the vinegar reduction and whisk over a pan of gently simmering water until the mixture begins to thicken and become frothy. Slowly trickle in the butter, whisking continuously – an electric hand whisk will help. If the butter is added too quickly the sauce will separate.
When you have added two-thirds of the butter, taste the sauce and add a little more, or all, of the remaining vinegar reduction. Then add the rest of the butter. The sauce should not be too vinegary, but the vinegar should just cut the oiliness of the butter. Season with salt and pepper, stir in the chopped wild fennel, cover with clingfilm and leave in a warm – not hot – place until needed. The sauce can be reheated over a bowl of hot water and lightly whisked again.
Put all of the ingredients for the court bouillon in a fish kettle or large saucepan – whatever you choose, it needs to be big enough to put the fish in; alternatively, you may want to cut the fish in half. Add about 2 litres of water, or enough to cover the fish, bring to the boil and simmer for 15 minutes. Place the sea trout in the court bouillon and simmer for 6-7 minutes and turn off the heat; leave in the court bouillon for another 6-7 minutes, checking that the fish stays slightly pink.
Remove the fish from the court bouillon and transfer to a warmed serving dish.