This recipe used to be one of my favourites when the children were small. It's foolproof (at least, I've never known it fail!) and in my opinion, is better than a chocolate Victoria Sandwich cake if you want a light sponge. The only reason I don't make it more often is that I prefer sturdier everyday cakes which last a bit longer - for some reason people always take larger slices from a sponge cake!
The basic recipe uses oil and milk instead of butter, and then a variable addition to give colour and/or improve flavour and texture. In some recipes it's a tablespoon of black treacle or golden syrup, but here it's two tablespoons of caramelised condensed milk.
I didn't want to go over the top with a frosting, so halved the recipe and just filled the sponge layers. The chocolate and condensed milk made a lovely fudgy mixture - I'm sure it would have made a great frosting!
The frosting/filling can be varied to suit the occasion - black cherry jam and fresh cream would make a nice gateau for a special occasion, although the sponge is very light, so may not take a really heavy filling well. I don't think the caramel made much difference to the flavour of the cake, so if you want to try the sponge without opening a tin or jar of caramel, try it with the black treacle, or molasses, instead.