Heat the olive oil over a medium to low heat in a heavy bottomed pan and add the garlic and anchovies. Cook gently until the anchovies have melted with the oil and the garlic is soft. About 8 minutes.
Add the lemon zest and butter, whisking in the butter so everything is combined. Add the parsley and give it a final stir.
Serve warm immediately and ideally in a dish over a flameto keep it warm. This is a deeply pungent and very grown-up sauce but the flavours can be softened by adding some extra butter.
Serving Suggestion
This ancient piedmontese dipping sauce is usually served with spanking fresh, crispy raw vegetables.