Wash the beans well and drain. Cook in a large pan of boiling salted water for about 15 minutes until tender. Drain and place in a vegetable dish. Keep warm, covered.
Meanwhile, prepare the sauce. Melt the butter in a pan, stir in the flour and cook gently for 1 minute, stirring. Remove from the heat and gradually stir in the stock.
Bring to the boil, and continue to cook, stirring, until the sauce thickens. Season and simmer for about 5 minutes.
Beat the egg yolks with the fresh cream in a small basin, add about 90 m (6 tbsp) hot sauce and stir until blended.
Remove the pan from the heat, add the egg mixture and stir well. Cook over a low heat without boiling until the sauce thickens a little more.
Remove from the heat and stir in the parsley and lemon juice. Adjust seasoning and pour over the broad beans.