This is a tough one, Tink. I grew up with Hot Milk Sponge & one that was flavored either with orange or lemon, but never a filled one. I checked my recipe books & found a couple with fillings (not lemon, but maybe you could adjust ingredients) but no instructions on how to get the filling in there.
Hot Milk Sponge
4 eggs
2 c sugar
2 c flour
1/2 tsp salt
2 tsp powder
1 c hot milk
1 tsp lemon juice or vanilla
Beat eggs until thick & lemon-colored. Slowly add sifted sugar & beat until well-blended. Add hot milk gradually, stirring vigorously. Add flavoring. Sift flour; measure & add salt & powder. Sift again. Add 2 tablespoons at a time, sifting slowly over egg mixture. Fold in flour with a whisk - until ingredients are well-blended. Pour into ungreased tube pan. Bake at 350 for 45 min. Invert pan to cool.
Filled Sponge Cake - without directions??
4 eggs (reserve 1 yolk for filling)
1 c flour
1 c sugar
1 tsp powder
Filling:
1 yolk
1 3/4 Tbl cornstarch
3/4 c milk
3/4 c sugar
Boil until thick, then add a lump of butter & flavor.
That's the entire recipe - sorry!
Here's another "filling" I found - it was listed as a separate recipe, not attached to any cake.
Filling:
1/2 box currants
1/2 box raisins
1/2 lb dates
1 coconut, grated
1 c English walnuts
1 c almonds
2 c sugar
1 c water
3 egg whites
Grind dried fruits. Grate coconut & chop nuts. Cook sugar & water until syrup reaches soft ball stage. Pour syrup over stiffly beaten egg whites. Beat until stiff & then add fruit & nut mixture. Spread on cake.