Instructions: Melt 1 oz of the butter in a pan until foaming; add the flour and cook this roux for 1-2 minutes. Add the milk gradually and bring the sauce to the boil, stirring constantly. Remove the pan from the heat.

Beat the egg yolks in a bowl and mix in a little of the sauce. Add this to the rest of the sauce, stirring well. Put the bowl over a pan of simmering water and stir in the remaining butter with the lemon juice and most of the zest.

Allow the sauce to heat gently until it begins to thicken, then season with salt and pepper.

Steam the broccoli for 5 minutes or so until it is cooked; drain it well and transfer it to a warm dish. Pour the sauce over, garnish with the remaining lemon zest and serve.

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