I tend not to make simple sponge cakes by the old fashioned creaming method these days as there is no need, and the all-in-one method gives more consistent results.
For a basic all-in-one Victoria sponge
Grease and base line 2 x 8" sandwich tins with baking parchment. It is important to grease the sides as it will help the cakes to rise. Preheat the oven to gas mark 4, fan 160 deg.
Weigh three eggs, then use the same weight in SR flour, sugar and tub Stork margarine. (for example if three eggs weigh 180 gm, then use 180gm each of flour, sugar and marge). Add a teaspoon of baking powder and combine the mixture until just mixed. Do not overheat the mixture as will will develop the gluten and prevent the cakes from rising.
Divide the mixture evenly between the tins and bake for about 25 minutes. Use a skewer to test if cooked. Remove from the oven and leave in the tins for a couple of minutes before turing out. When cool sandwich together with whatever takes your fancy - jam, jam and cream, buttercream, lemon curd and mascarpone etc. Sift a little caster sugar on top.
Notes: I always add a little vanilla extract to the cake mixture for a plain cake, or grated lemon/orange rind for a citrus cake. I use tub Stork because I can use it straight from the fridge, it gives excellent results and doesn't affect the taste of the cake. Besides, Queen Mary Berry uses it as well.