Step 1

In a heatproof bowl set over simmering water (double boiler), melt the chocolate and butter gently. Stir occasionally until smooth. Remove from heat and let it cool slightly for about 10-15 minutes.

Step 2

When slightly cooled, whisk in the sugar and the egg yolks, followed by the vanilla extract.

Step 3

In a separate large mixing bowl, beat the 6 egg whites and salt to a stiff peak - meaning peaks will stand straight up when the beaters are lifted.

Step 4

Using a large rubber spatula, gently fold the whipped egg whites into the chocolate mixture in three additions, being careful not to deflate the batter. Stop when the texture is just uniform – do not over mix.

Step 5

Line a  8.5x4.5-in loaf pan (21.5x11.5cm) with plastic wrap (bottom and edges). Pour in the mixture and cover with another piece of plastic wrap – the wrap should touch the whole surface. Refrigerate for at least 6 hours, preferably overnight. For a firmer texture, freeze instead and let sit at room temp 15–20 min before slicing.

Step 6

Unmold onto a serving plate. Slice with a warm knife, and serve with toppings of your choice.