The one I use, which has never failed me yet (hah! Hostage to fortune!) is:
Weigh 3 room-temperature eggs, then use this quantity for other ingredients, butter, caster sugar and SR flour as follows.
Pre-heat oven to 180C/350F/Gas 4. 10 degrees less for fan oven.
Grease and flour (or line with baking parchment) 2 x 18cm/7in cake tins
1. Cream butter and sugar until fluffy and white.
2. Beat in eggs one at a time, adding a little flour if the mixture looks like curdling (it shouldn't if the eggs aren't too cold), along with 1tsp vanilla essence.
3. Fold in flour with a metal spoon. Add a little milk if mixture seems stiff.
4. Divide mixture between the prepared tins, levelling gently.
5. Bake for 20-25 minutes, or until golden-brown on top and a skewer comes out clean.
6. Remove from the oven and set aside for 5 minutes to firm, then remove from the tin and peel off the paper. Place onto a wire rack to cool.
Sandwich the cakes together with jam, or whipped cream and berries, or buttercream.