Langoustines with watercress and pastis hollandaise

Method

1. Arrange the langoustines on a platter. Put the shallot, peppercorns, mace, vinegar and 130ml water in a small pan. Bring to the boil, then reduce by around three quarters. Set aside in a heatproof bowl.
2. Meanwhile, put the watercress in a colander and pour over a kettle of boiling water. Leave to wilt slightly, then pat dry between pieces of kitchen paper. Chop very finely or whizz in a food processor with a splash of double cream.
3. Put the bowl containing the vinegar reduction over a pan filled with hot water, set over a medium heat (don’t let the water touch the bowl). Using a balloon whisk, beat in the egg yolks until beginning to froth. Pour in the butter in a thin stream, whisking. The sauce should start to thicken after a minute; if it doesn’t, stop adding the butter and whisk the sauce for a minute to thicken up. If it starts to look greasy, whisk in a splash of cold water and reduce the heat.
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5. Once all the butter has been added, the sauce should be smooth, glossy and thick. Stir in the watercress and pastis, then taste and add lemon juice if needed. Serve the sauce warm in a bowl alongside the langoustines, with extra watercress and lemon wedges.