Preheat the oven to 180ºc/160ºc fan and line two round 8” tins with parchment
Beat together the butter and sugar until fluffy
Add the eggs, and flour, and buttermilk and mix
Split between the two tins
Bake for 30-35 minutes, and cool fully
Whilst the cake cools, add the sugar and water to a pan
Heat on a low heat, stirring gently, until the mixture isn’t cloudy anymore and the sugar has dissolved.
STOP STIRING, and turn up the heat to boil.
Boil until the mixture becomes a deep amber colour - keep an eye on it as it takes a while, and will suddenly start turning. Do NOT stir it.
Remove from the heat and mix in the butter - it'll bubble quite a lot but keep whisking
Add in the cream and whisk again
Add the vanilla/salt and stir through
Leave to cool fully for a few hours so it starts to thicken (reserve a little for decoration if you want). You might need to cool it in the fridge/freezer to thicken quicker if the weather is hotter or it's taking too long.
Once fully cooled, whip the caramel for a few minutes until it holds itself and lightens in colour
Spread over the bottom cake, and the top cake, and add any extra caramel if you want
Notes
This cake is safe to store at room temperature on a cool day for 2-3 days
On a super hot day it may need to be stored in the fridge so that the caramel doesn't melt