For the dill sauce, cook one finely diced shallot with a pinch of salt in 50ml of dry white wine, 50ml of white wine or cider vinegar and 50ml of water. Cook until the liquid is almost evaporated and the shallots are soft, then pass through a sieve. Heat the resulting puree on very gently heat and whisk in 100g of salted butter, one walnut-sized piece at the time. Take care to keep the heat very low; you want the mix to be at approximately 80C – hot, not boiling.
Remove from the heat and whisk in the two egg yolks. Keep whisking until the sauce has cooled down and the egg yolks are cooked in the residual heat.
Add a generous amount of finely chopped fresh dill. Keep at room temperature.