Preheat the oven to 200°C (fan 180°C)/400°F/ gas mark 6. Grease 6 ramekin dishes.
Melt the chocolate in a heatproof bowl set over a saucepan of barely simmering water, making sure the surface of the water does not touch the bowl. Stir in the rum, if using. Remove from the heat and add the crème fraîche, then the egg yolks.
In a large, clean, dry bowl, whisk all the egg whites and the salt to soft peaks.
Fold one-quarter of the egg whites into the chocolate mixture, then fold in the remaining whites.
Fill the prepared ramekins to the top with the mixture, then clean the rims using your finger and thumb. Place on a baking sheet and bake in the oven for 10–12 minutes, or until nicely risen. Dust with icing sugar and serve immediately.
Tip: For a delicious party trick, serve your soufflés with an ice-cream drop. Before you make the soufflés, scoop out 6 balls of good-quality vanilla ice cream and place on a freezer-proof plate. Keep in the freezer until ready to serve. When serving the soufflés at the table, drop an ice-cream ball into each soufflé.
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