This recipe is from a small booklet called The Mazola Method for Pperfect Baking, which came free with, you guessed it, Mazola corn oil, about a million years ago (er, 1970s some time probably).

FEATHERLIGHT SPONGE CAKE

5 oz. plain flour
1 oz. cornflour
2 level tsp. baking powder
0.5 level tsp. salt
5 oz. caster sugar
2 eggs
3.5 fl. oz. (5 tbsp) Mazola Corn Oil
3.5 fl. oz. (5 tbsp) water

Line bottom of two 7-inch sandwich tins with greaseproof paper and grease lightly.

Sieve dry ingredients into a bowl.

Separate yolks from whites of eggs. Mix corn oil, yolks and water together lightly with a fork. Stir the mixture into the dry ingredients and beat well to form smooth, slack batter.

Whisk egg whites until stiff and fold lightly into mixture.

Turn into tins and bake in moderately hot oven (375 degree F / Mark 5) for 25-30 minutes. Cool on wire tray.

Sandwich together with jam and dust with caster sugar or top with icing.

Variations:
Chocolate flavour -- replace cornflour with equal quantity of cocoa.

Coffee flavour -- add two teaspoons instant coffee powder to liquid ingredients and mix well before combining with dry ingredients.

Orange or lemon flavour -- add the grated rind of half an orange or half a lemon to the ingredients.

Notes from source:
i. You don't have to use Mazola Corn Oil; that bit is purely a marketing gimmick. I've used bog-standard cheap vegetable oil, supermarket own-brand corn oil, real Mazola, and Mazola 'lite', and never noticed any difference.

ii. I often don't bother to sieve the dry ingredients, and at the moment I don't even *own* a sieve (although I did have to shove the cocoa for the chocolate version through a tea-strainer because it was so lumpy!).

iii. The 'folding lightly' (which scares a lot of people off lots of recipes) is less fragile than people seem to think, and will cope with a fair amount of inexpert folding (like what I do!) -- basically just so long as you don't *beat* it or mix too hard, it'll be fine. The point of it is to keep the air in the whisked egg whites -- this is what makes the sponge light and fluffy. The worst that will happen if you do it badly is that your sponge will be a bit heavy.

2. The 25-30 minutes is by no means exact and will largely depend on your oven. (By the way, that 375'F is equal to 190'C.) Fan-assisted ovens generally need 10 degrees knocking off the temperature (this is a general rule, not just applicable here; apologies to anybody for whom this is a really obvious thing to point out). Basically, though, cook it until it's done (see below).

3. How to tell if cakes like this are cooked: stick a sharp knife or a skewer or something in it, right in the middle because that's where it's likely to be thickest (and therefore take longest to cook). If the knife comes out clean the cake's probably done; if the knife comes out sticky it probably needs a bit longer.

4. If you want to cook this cake in one tin, let me assure you that it does work (but takes a bit longer to cook), and even works fine with double quantities, although cooking time will need adjusting (takes about an hour in my oven). Double quantities does a 10" cake about right. I've never tried more than double, probably not advisable since even double-quantities is getting dangerously near to burning on top by the time it cooks in the middle.

5. You really want the egg whites to be stiff enough to stay in peaks when you lift a bit up. This is what makes the sponge light. I suspect a sponge cake with only partially-stiffened egg whites would be edible but a bit flatter and heavier.

6. Baking parchment (or greaseproof paper, which is cheaper and just as effective) really does help -- I grease both the inside of the tin and the inside of the paper with margarine. The latter stops the cake sticking to the paper and the former makes the paper stick to the tin so you can pour the cake mix in without the paper falling in! However if you don't have baking parchment or greaseproof, it's still do-able; just make sure the cake tin is really well greased, and when it's cooked slip a knife round the side before trying to get the cake out.

7. I don't remember ever having tried the coffee or citrus versions. The chocolate one is great though.