sponge cake recipe please!

[Hopefully]

Have just had my first ever failed sponge recipe, and I've lost my old foolproof recipe. Have plain flour and baking poweder or self raising....

Help! Need to make cake tonight (not that I'm leaving things late for birthday party tomorrow or anything)

2oz flour, sugar, marg and one egg
increase as you need eg 6oz everything plus 3 eggs will fill 2 x7 inch sandwich tins

ps use self raising
gas 5 or 190ish electric 20 mins ish

Thankyou thankyou thankyou. I think it was the crappy recipe calling for plain and baking powder that ruined me. Clearly I cannot be trusted to measure out a teaspoon accurately despite my bunting cupcakery Nigella measuring spoons.