This millionaire shortbread cake recipe takes a classic sweet treat and converts it from biscuit to sponge cake! So you still get the rich chocolate and smooth caramel layers, but with vanilla cake instead of shortbread biscuit!
You can begin cooking the caramel once the cakes are in the oven.
Put the butter, light soft brown sugar and condensed milk in a large, heat proof bowl.
Heat in the microwave for 2 minutes to melt everything together. Stir, then continue the heat and stir for 3 further 2 minute blasts (to a total of 8 minutes). Be extremely careful and use oven gloves and care when handling the bowl as the caramel will bubble and reach almost 120C (250F). Stir by reaching the silicon spatula into the microwave if possible and safe to do so so that you can avoid moving the bowl any more than necessary.
When you've finished cooking the caramel, leave it in the microwave to cool. It will thicken as it cools.
Make the sponge
Grease and double line a tall 18 cm (7 inch) cake tin.
Preheat the oven to 180C (160C fan, 350F).
Put the sugar and butter in a large mixing bowl and whisk together until pale.
Add the eggs, vanilla and milk and whisk again
Sift in the flour then fold together.
Spoon into the lined tin and level off.
Bake for 1 hour minutes until golden. Leave to cool in the tin until safe to touch, then release onto a wire rack to cool completely.
Make the milk chocolate ganache
While the cakes are cooling, you can make the ganache.
Put the cream and vanilla in a heatproof bowl and heat in the microwave in 30 second blasts until almost boiling.
Add the chopped milk chocolate and allow to stand for 1 minute, then stir until smooth and silky.
Assemble the cake
Important note: when assembling the cake, if the ganache or caramel are at all warm, they will be too loose to work with, so let them cool. Likewise, if they become too cool, they will be too stiff to work with. You can loosen them by placing them in the microwave for a few seconds, but do so very sparingly as they can easily become too warm again and melt.
Cut the cake into two halves using a sharp serrated knife.
Place the bottom cake half on a board, cut side up.
Top with a third of the caramel, then spoon a quarter of the ganache on top.
Put the second cake half on top, cut side down.
Spoon another layer of caramel on top, this time more generously - you might not need it all.
Spoon the remaining ganache onto the cake and spread all over the top and sides to cover the cake.
To serve, allow to set for at least an hour, then cut the cake into slices with a sharp, serrated knife.
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Notes
Carnation caramel, which is popular in the UK, is not thick enough to be used in place of the homemade caramel in this recipe. However, some brands of caramel / dulce de leche are very thick. If you feel that you have a found a jar of caramel that will hold up to slicing, you can use that in place of the caramel stage.