Years ago I had a pudding which was cake on top and lemony sauce underneath. I had a go at the recipe, using a recipe from UKTV as a start. The BBC recipe needed more lemons than I had, and I thought it would be possible to test the structural qualities of the cake with the first recipe.
55g butter, softened
zest and juice of one lemon - I would definitely use at least two next time as very mild flavour
2 large eggs, separated
65g flour (recipe called for 55 but the mix was so sloppy I added 10g)
1 tsp baking powder
Cream butter, sugar and zest until light
Add egg yolk, lemon juice, flour and baking powder and mix
whip egg white until stiff and fold into batter
Place in a buttered dish and bake in a 180C (fan) oven for 40mins. Place the dish into a roasting pan and half fill with water to produce a gentler cooking environment.
This produced a pleasant, mildly lemon-flavoured, soft fluffy pudding. It didn't really produce the separate sauce at the bottom that I remember. I'll have to try it with less flour even though the batter looks as if it would never make a cake of any sort! Two lemons with the same amount of the other ingredients may well be sufficient to give a zingy flavour.