Preheat the oven to 180°C, 350°F, Gas 4, and base-line 2 x 18cm/7in sandwich tins with baking parchment.
Sift the self-raising flour, cocoa powder and bicarbonate of soda into a large mixing bowl and stir in the caster sugar.
Pour the corn oil and milk into a measuring jug, add the eggs and 1 tsp of the vanilla extract and whisk lightly to mix.
Beat 2 tbsp of the Carnation Caramel until smooth and whisk it into the egg and oil mixture. Add the wet ingredients to the dry ones and mix well to combine. Pour the cake mixture – which will be quite wet – into the prepared tins and bake in the centre of the preheated oven for 20-25 minutes, until the top of the cake is springy to the touch. Leave the cakes to cool a little in the tins, then turn them out onto a wire rack, peel off the baking parchment and cool completely.
Melt the chocolate by placing it in a microwaveable bowl and heating very gently in short bursts of 10 seconds on HIGH in the microwave, stirring until smooth, or place it in a heatproof bowl set over a pan of barely simmering water, stirring until melted. Add the remaining Carnation Caramel and vanilla extract and beat well until glossy. Sift in the icing sugar and mix thoroughly.
Place one cake half, upside down, on a plate, spread with a generous dollop of icing and top with the other cake half. Use the remaining icing to completely cover the top and sides of the cake. Arrange the sugar flowers around the top of the cake, and leave the icing to set. Cut cake into slices to serve.