Preheat your oven to 220°C/200°C fan.

Break the milk and dark chocolate into small pieces. Place in a large heatproof bowl along with the butter. Sit over a pan of gently simmering water, keeping the base of the bowl clear. Once the chocolate has melted, remove from the heat, stir until smooth and set aside until a little cooler. In another bowl, break up the white chocolate and melt, set aside.

Put the eggs into a large bowl and add the sugar. Whisk for a few minutes using a electric hand whisk until you get a white very fluffy mousse, you should be able to leave a trail of mousse that lasts for a second or so. Pour the cooled chocolate onto the mousse. Use a large metal spoon or spatula to cut into the mix and lightly fold together with a figure-of-eight movement until combined. Pour into the pastry case. Spoon over the melted white chocolate, creating whatever pattern you desire.

Bake for 7-10 minutes until the chocolate is just set and is a bit firmer than a mousse. Shuffle the tin the check its firm in the centre. Sit on a rack for 5 minutes, lift it out of the tin and leave to cool. It’s great at room temperature but just as good refrigerated.