To serve 4 you will need 1kg of freshly steamed asparagus. For the sauce, 3 egg yolks, 200g of almost melted butter, and a shot of lemon juice. Put a pan of water on to boil and find a glass or heatproof china bowl that will fit neatly into it without actually touching the water. Add the yolks and a splash of water. Whisk, pouring in the melted butter, slowly at first as if you were making mayonnaise, then as the sauce thickens up, a little faster. Once it is thick and creamy, squeeze in a little lemon juice and stir in a pinch of salt. No pepper. The sauce can be used as it is.
Hollandaise sauce is a notorious curdler. One minute you have a silky sauce, the next scrambled eggs. The heat should never be too hot, so use a heatproof glass bowl over lightly simmering water rather than make it directly in a saucepan. Have a shallow sink of cold water to hand. If your sauce looks as if it is about to separate, quickly remove it from the heat, dunk the pan into the water and whisk very hard. It will usually come round. If it still fails then start again with a clean bowl and fresh egg yolks and add the curdled mixture slowly to the new eggs, beating all the time.
Grated orange zest, perhaps with the last of the blood oranges, is a well-known elaboration. Other ideas include adding grated Parmesan over the spears – it is good with this sauce. My favourite is to add chopped tarragon and a dash of tarragon vinegar to the sauce.