To make the sponge cake, oil two 8" cake tins and line with lightly oiled parchment (or aluminium foil) to cover the bottom and sides to a height of about 2". This will allow you to lift the entire cake out of the pan without breaking it. The oil helps the parchment stick to the pan, so it doesnu2019t slip while pouring in the batter.
Mix the dry ingredients together in a large bowl. Add the butter, water, and lemon juice and beat well with an electric mixer for about a minute. Add the remaining ingredients and beat again.
Pour the batter into the lined cake tin and bake at 190C for about 25-30 minutes, until the edges are golden brown and the top is lightly browned, and the center springs back to your touch. Allow to cool in pan until just warm.
This makes 2 sponge layers. Repeat to make as many layers as you want (I made 6 layers and one rectangular layer which I cut into smaller rectangular pieces for the caramel sponge layer)
The Eggless Chocolate Buttercream can be made in advance and keep chilled in the fridge. Dissolve the cornstarch in about 2 tbsp of water. Melt the chocolate in a large bowl, over a double boiler. Add the sugar to the melted chocolate and whisk till well incorporated into the chocolate.
Now add the dissolved cornstarch and keep whisking till the chocolate thickens. Take the bowl of the heat and cool to room temperature. The chocolate mixture will thicken some more.
The beat in the butter, a few tbsps at a time into the chocolate mixture with an electric mixer till soft and velvety. Chill in the fridge till ready to use.
To make the Caramel Topping, put all the ingredients in a pan and stir till the sugar dissolves. Now bring the mixture to boil, stirring gently once in a while. Once the mixture starts boiling, turn down the heat to medium and allow the sugar syrup to caramelize and turn amber. Stir gently if you must but do not agitate the syrup.
This syrup is meant to be cooked till amber, but I didn't want a hard caramel layer. So I took the syrup off the heat when it was a deep golden colour and generously spooned the syrup over the rectangular sponge pieces. Allow to set.