Beat the egg yolks with the sugar, the juice of one and the grated zest of half the lemons until creamy and gradually add the remaining ingredients.
Whip the egg whites with 1 pinch of salt until stiff peaks form and mix gently. Pour everything into a well-buttered and floured custard dish and cook the tightly closed custard in a lightly simmering water bath for about one and a half hours.
Fill the mold only to about two-thirds full, as the pudding will increase in volume as it cooks.
To serve, turn the pudding out onto a plate (perhaps wrap the mold briefly with a cold damp kitchen towel to help the pudding release from the mold). Serve with compote or fruit sauce.