Chop the two kinds of chocolate in small pieces and melt over low heat. To melt the chocolate it is best to use a bain-marie (or double boiler), a piece of equipment used to heat the chocolate gently and gradually to fixed temperatures so that it doesn't burn. If you don't have a Bain-marie, break the chocolate into small pieces and drop into a heatproof bowl. Set the bowl over a small saucepan about a quarter full with hot water and place the bowl on top so that it rests on the rim of the pan (the bowl should not touch the water). Place the pan, with the bowl on top, over low heat until the chocolate has melted, whilst stirring occasionally.

In the meantime, heat the milk into a microwave, until lukewarm.

Pour the lukewarm milk over the melted chocolate and blend gently with a wooden spoon. Remove the pan from the stove and add the yogurt. Blend the mixture with light circular movements, until combined.

To serve, place some crushed biscuits on the bottom of a glass or a bowl and top with the yogurt chocolate mousse. Layer the ingredients, according to your preference and top with some more biscuits or crushed white chocolate. Enjoy!