Pour the wine, vinegar and shallots into a saucepan set over a medium-high heat. Bring to a simmer and cook until the liquid has reduced to about 1-2 tbsp. Strain the mixture into a jug and discard the shallots. Pour 1 tbsp back into the saucepan.

Put the pan over a low heat and vigorously whisk in the butter, a cube at a time, only adding another cube after the previous addition has melted into the sauce and emulsified. Keep a close eye on the heat – if the sauce starts to look greasy or you can see obvious streaks of butter, remove from the heat and continue whisking, but don’t add any more butter until it looks cohesive again (see tip below).

Once at least half of the butter has been added, starting whisking in two cubes at a time. The sauce should start to look thick and glossy, and will take on the consistency of double cream. The process will take about 20-25 mins. Season to taste with another splash of the initial reduction and salt and pepper. Serve immediately.