Cut the butter into small dice and put into the bowl of a food mixer with the caster sugar. Beat till light and fluffy. Sieve together the flour, baking powder and cocoa. Don't miss this step - it is really important that the dry ingredients are well mixed. And yes, the recipe does contain self-raising flour and baking powder - just go with it.
Line 2 x 20cm sponge tins with a disc of baking parchment. Set the oven at 170C/gas mark 5. Crack the eggs into a small bowl, beat them briefly to mix, then stir in the milk.
Introduce the flour mixture and the eggs and milk to the butter and sugar, adding a little of each at a time, with the mixer going all the time till you have a smooth mixture.
Divide the mixture between the two cake tins and smooth the surface. Bake for 35-40 minutes till risen. Test with a metal skewer. If it comes out moist but clean, without any mixture stuck to it, then they are ready.
Remove from the oven, leave to settle for 15 minutes, run a palette knife around the edges, then gently turn out on to a cooling rack. When the cakes are almost cool, peel off the baking parchment.
Add the mascarpone, icing sugar, maple syurp to a mixing bowl and whisk together. Whilst whisking, add the double cream, continue mixing until smooth and soft peaks are formed.
Sandwich the cake together with half of the filling and a layer of salted caramel. Then pipe the remainder of the cream on top. Finish with a sprinkle of grated chocolate and toasted almonds.