Sauce béarnaise

• 200 g (7 oz/1 scant cup) unsalted butter
• 30

You need to start by clarifying your butter (butter alone will be too liquid to use). Place it in a small, heavy-based saucepan over a low heat and allow it to melt slowly, then continue to heat it until it starts to foam. When foaming, remove the pan from the heat and leave it to stand for a few minutes so that the white solids sink to the bottom of the pan. Pass the butter through a fine siev