Preheat the oven to 170°C/gas mark 3. Line a 30cm loaf tin with baking paper.
Beat together the butter and sugar until pale and fluffy then add in the eggs until fully incorporated.
Gently fold in the flour and the cocoa powder and mix until fully incorporated, add whole milk if mixture is too thick.
Pour half the mixture into the prepared tin, then spoon in some salted caramel sauce in the middle then add the rest of the cake mixture.
Bake for 45–50 minutes, until a metal skewer inserted into the middle of the cake comes out clean. Leave to cool on a wire rack