Step 1

Place the dark chocolate and the butter in a heatproof bowl and melt them on a low setting in the microwave, making sure to check the mixture every 20 seconds and stir it so it doesn't burn.

Step 2

Once the dark chocolate and the butter are completely melted, pour in the Guinness and whisk quickly to combine.

Step 3

Add the egg yolk, and whisk the mixture again to combine, before leaving the chocolate mixture to cool completely.

Step 4

In a clean bowl, whip up ½ cup whipping cream, and fold the cream into the cooled chocolate.

Step 5

In another bowl, beat the egg white until it is foamy and stiff. Then, slowly add in the two tablespoons of sugar, one at a time, until the sugar is completely mixed in. The mixture shouldn't feel grainy between your fingers. If it does, keep beating the mixture until it feels smooth.

Step 6

Gently fold the egg white into the chocolate mixture, and divide the mixture between 4 dessert glasses and chill in the fridge.

Step 7

In a clean, heatproof bowl, combine the white chocolate and ¼ cup whipping cream and slowly melt them in the microwave, making sure to check the mixture regularly so it doesn't burn. Once it is completely melted, set it aside for 15 minutes until it has cooled and thickened.

Step 8

Whip up the final ¼ cup of cream and fold it into the cooled white chocolate mixture, then spoon this on top of the chilled chocolate mousse.

Step 9

Serve chilled, and if you like, top with chocolate candy.