i don't know where this came from i think it just manifested in my parents' house one day on a buttercream-stained notecard

• 4 eggs
• 225 g caster sugar
• 225 g self-raising flour
• 225 g butter
• 1 tsp baking powder
• About half of a jar of nice jam (see notes)
• About 1 tsp vanilla extract
• If making a buttercream icing:
  • 100 g butter
  • 200 g icing sugar
  • 2 tbsp milk
• If making a whipped cream filling:
  • About half a small container of whipping cream (like 200 ml?)
  • A few drops of vanilla extract
  • A tbsp or so of caster sugar

1. Preheat oven to 160 °C (fan) and grease/line two 8-9" cake tins.
2. Cream together butter and sugar.
   
   225 g butter
   225 g caster sugar
   
3. Add vanilla and then beat in eggs one by one.
   
   About a tsp of vanilla extract
   4 eggs
   
4. Combine dry ingredients in a different bowl and then sift in to the rest.
   
   225 g self-raising flour
   1 tsp baking powder
   
5. Split the mixture across two cake tins.
6. Bake for like 25 min, till a skewer inserted into the centre can be removed without any batter sticking to it.
7. Transfer to a cooling rack and remove the baking paper while still warm.
8. Make a filling.
   • For a buttercream filling: mix butter, icing sugar, and milk till smooth and thick.
     
     100 g butter
     200 g icing sugar
     About 1 tbsp milk - add more as needed
     
   • Or, for a fresh cream filling: add a bit of sugar and vanilla to whipping cream and whip with an electric whisk until thick and nearly solid.
     
     About 200 ml whipping cream
     A tbsp or so of caster sugar (eyeballed)
     A few drops of vanilla extract
     
9. When the cake is fully (FULLY) cooled, cut the top off one of the halves so that it is flat then cut each half in half again (if possible).
10. Warm about half a jar of jam till easily spreadable. Add jam and cream to each of the exposed layers. Leave a gap of about 2 cm from the edge - the filling will squash out to fill this when the cake is assembled.
    
    About half a jar of jam
    Prepared cream filling
    
11. Sandwich all parts together gently.
12. Dust the top of the cake with sifted icing sugar.

• Seedless jam is better but whatever you like. Strawberry is classic; raspberry is also good; plum/damson are basically impossible to find as smooth jam (mostly just as conserves) but are also pretty good ↑
• If you're not able to cut the halves in half again, it's absolutely fine to just have one thick layer of jam+cream in the centre - it's just nicer to have a few thinner layers with better distribution, so you have less chance of getting a big mouthful of dry sponge all by itself. Could try splitting the batter across 3 or 4 trays instead of 2, if you have trays spare.
• A fresh cream filling is nicer (imo). If using, the cake should be refrigerated. A buttercream filling lasts slightly longer and is easier to transport and store as it is slightly more rigid. You could also just buy a tub of buttercream filling but honestly if you're going to the trouble of making the cake why wouldn't you take 5 min extra to make a tastier filling