Preheat your oven to 180?C/350?F and grease and line two 8-inch cake tins.

In a large bowl, combine the butter, oil, brown sugar, and vanilla. Beat on high speed for 5 minutes.

Add 2 eggs to the mixture, whisk in, then add the remaining 2 eggs and whisk until combined.

Add the self-raising flour and the milk/coffee mixture. Whisk until a smooth batter forms.

Pour the batter into the prepared cake tins, spread evenly, and bake for 40-45 minutes or until a toothpick comes out clean.

While the cakes are baking, prepare the milk mixture by heating milk, coffee, and brown sugar over medium heat until the coffee dissolves. Allow to cool.

Once the cakes are done, pour the milk mixture over them while they are still warm, then let cool completely in the tins.

For the caramel, heat 1/3 of the granulated sugar in a pot over medium heat, stirring constantly until it starts to melt.

Gradually add the remaining sugar, continuing to stir until fully melted and amber in color.

Remove from heat and whisk in the butter, then slowly pour in the warm double cream, mixing well. Add salt and sieve to remove lumps, then cool completely.

Once the cakes and caramel have cooled, assemble the cake by placing one layer on a plate, spreading buttercream on top, and piping a border. Pour cooled caramel in the center.

Place the second layer of cake on top. Decorate as desired with buttercream and caramel, and finish with a sprinkle of ground cinnamon.