Ingredients:

Biscuit base:

• 70 g digestive biscuits
• 25 g melted butter (2 tbsp)
• 1 ½ tbsp castor sugar

Chocolate brownie:

• 90 g castor sugar
• 1 egg + 1 egg yolk
• 60 g butter, softened at room temperature
• 60 g dark chocolate 
• 40 g flour
• Pinch of salt

Red velvet cake:

• 60 g flour
• 5 g cocoa powder (1 tbsp)
• 60 g castor sugar
• ¼ tsp salt
• 65 g vegetable oil
• 1 egg
• Red food colour (as required)
• 1 tbsp yogurt
• ¼ tsp vanilla extract
• ¼ tsp baking soda
• ½ tsp white vinegar

Marshmallow icing:

• 1 egg white
• 70 g castor sugar (approx. ⅓ cup)
• ¼ tsp white vinegar or lemon juice
• Pinch of salt

Process:

Prepare the biscuit base:

1. Grease and line a loose-base cake tin with baking paper.
2. Ground the biscuits to a fine crumb.
3. Mix in the melted butter and castor sugar.
4. Spread the mixture evenly in the cake tin and press it in firmly using your fingers or the back of a spoon. 
5. Set the tin in the fridge so the base hardens.

Make the brownie batter:

1. Melt the dark chocolate and butter over a double boiler or in the microwave and cool it down.
2. Whisk together the eggs and sugar till airy and pale.
3. Add in the melted chocolate and butter and mix.
4. Sift in the flour and salt and gently fold it in.
5. Pour the batter over the biscuit base and set aside.

Make the red velvet cake batter and bake:

1. Preheat oven to 175°C.
2. Sift the flour, cocoa, sugar and salt into a bowl.
3. Add in the vegetable oil and egg and whisk together.
4. Mix the yogurt, red food colour and vanilla in a separate bowl. 
5. Add the yogurt mixture to the main batter.
6. Mix vinegar and baking soda in another bowl, then mix it into the main batter. 
7. Pour the red velvet batter using a spoon over the brownie batter in the tin. 
8. Bake in at 175°C for 30-35 minutes.
9. Allow the cake to cool down while you prepare the marshmallow icing.

Make the marshmallow icing and decorate the cake:

1. Set some water to boil in a saucepan.
2. Mix the egg white, castor sugar, vinegar and salt in a heatproof bowl.
3. Bring the water in the saucepan down to a simmer and then place the bowl over it and start to whisk using an electric mixer.
4. Whisk for 6-7 minutes until the mixture is double in quantity and all the sugar has dissolved. (Feel the mixture between your fingers for any grains of sugar.)
5. Remove the bowl from heat and add in the vanilla and whisk for another 1-2 minutes until you have frosting like consistency.
6. Pipe the frosting onto the brownie using a piping bag fitted with a round nozzle.
7. Use a blow torch to toast the marshmallow frosting or place it under the hot grill of an oven to brown.
8. Slice and serve warm or at room temperature.