Place the egg whites and sugar in the stainless steel bowl of your food mixer and stir over a pan of water (making sure the base of the bowl does not touch the water) at a moderate heat until the mixture is hot and the sugar dissolved (around 65C). The sugar and heat kill off any bacteria and effectively sterilise the mixture.

Then attach it to your food mixer and whisk for about 5 minutes until very thick, holding its shape and cooled.

Melt the chocolate (either in the microwave or over a pan of water) and allow it to cool a little. Add this to the meringue and beat it in, until fully mixed.

Beat the butter into the meringue in small cubes. Stop whisking when the butter is thoroughly mixed through and the mixture has thickened.

If it starts to look coarse and rough, then warm it slightly in the microwave and beat it again until creamy.

If the cream is too runny, chill it for a few minutes and then beat it again to thicken.