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Rahul’s Edible Rock Garden Chocolate Cake

This moist chocolate cake is surrounded by crunchy chocolate soil and decorated with a piped garden. Feel free to be creative – take the opportunity to design your own garden!   

Serves: 20 

Hands-on time: 1 hour 20 minutes  

Baking time: 30 minutes  

Skill level: Needs skill  

For the chocolate sponge: 

100g cocoa powder  

120ml boiling water  

600g dark brown soft sugar  

200g baking margarine or softened salted butter 

6 eggs  

350g self-raising flour  

2 tsp baking powder   

For the Italian meringue buttercream: 

200g caster sugar  

4 egg whites 

250g salted butter, diced 

250g unsalted butter, diced   

1 tsp orange extract  

1 tsp vanilla extract 

1 tsp lemon extract  

green and red food-colouring gels or pastes  

For the chocolate soil: 

100g caster sugar  

75g 70% dark chocolate, roughly chopped 

You will also need:  

20cm round sponge tins x 2 and 15cm round sponge tins x 2, greased and base-lined with baking paper  

Sugar thermometer 

Plate lined with baking paper 

2 small disposable piping bags 

Step 1 – Heat the oven to 180°C/160°C fan/350°F/Gas 4.  

Step 2 – Make the sponge. Put the cocoa and boiling water in the bowl of a stand mixer fitted with the beater. Beat together, then add the remaining cake ingredients, except the colouring, and mix at medium speed to a soft batter.  

Step 3 – Divide the mixture between the prepared tins so that the depths of the cakes are equal. Bake for 25–30 minutes, or until a skewer inserted into the centres comes out clean. Leave the cakes to cool in the tins for 5 minutes, then turn out onto a wire rack to cool completely. 

Step 4 – Meanwhile, make the Italian meringue buttercream. Place the caster sugar and 100ml of water in a medium pan and over a medium heat. Heat gently until the sugar has dissolved, then increase the heat and boil until the syrup reaches about 110°C on a sugar thermometer.  

Step 5 – Whisk the egg whites in the clean bowl of a stand mixer to soft peaks. Keep the whisk running and, when the sugar syrup has reached 121°C, remove the pan from heat and slowly pour the syrup in a thin, steady stream into the whisking egg whites.  

Step 6 – Continue whisking until the outside of the bowl is at room temperature and the meringue is very thick and glossy.  

Step 7 – When the mixture is at room temperature, start adding cubes of salted and unsalted butter, whisking after each addition to make a smooth and thick buttercream. Add the orange, vanilla and lemon extracts and mix thoroughly. Cover, and chill until firm. 

Step 8 – Make chocolate soil. Heat 2 tablespoons of water and the sugar in a small pan over a medium heat until the sugar dissolves. Increase the heat and boil the mixture until it just starts to turn golden around the edges – about 135°C on the sugar thermometer.  

Step 9 – Stir in the chopped chocolate – it will immediately form clumps and crumbs. Tip onto the lined plate and leave to cool. 

Step 10 – To assemble, sandwich the 2 larger cakes with 3 tablespoons of the buttercream, spread evenly, and place on a plate. Spread 1 tablespoon of buttercream on top.  

Step 11 – Sandwich the 2 smaller cakes with about 2 tablespoons of buttercream and stack these on top of the larger cakes.  

Step 12 – Place 6 tablespoons of buttercream in a small bowl and add green food colouring to make a leaf colour. Place 4 tablespoons of plain buttercream in a second bowl and colour this flower-like red.

Step 13 – Spread the remaining plain buttercream around the top and sides of the stacked cake.  

Step 14 – Place the red and green icings in separate small disposable piping bags. Snip off the tip of the red icing and make a v shape cut in the end of the bag of green icing.  

Step 15 – Pipe green leaves around the sides of both cake layers and a few on the top, adding red dots to make flowers. Sprinkle the soil around the bottom of each cake layer and sprinkle a little on top. 

Chill the cake and serve within 2 days.