Ingredients  
120ml white wine
50ml white wine vinegar
½ tbsp shallots
225g diced butter

Method  
Bring the wine, vinegar and shallots to the boil and reduce until you have 1 tbsp of liquid. Strain and return to the heat. Add the butter one cube at a time whisking constantly until you have 2 pieces left. It should be thick and glossy. Add the remaining butter off the heat.