1 Preheat the oven to 200 ̊C, gas mark 6; set a baking tray on the top shelf of the oven. Melt 10g butter and brush the insides of 2 x 225ml ramekins to the top of the rims. Leave it to cool slightly, then brush again.
2 Put the chocolate in a bowl. Heat the milk, cream, vanilla and 20g sugar in a small pan until steaming. Pour it over the chocolate; stir until smooth.
3 Wipe the pan out, then melt the remaining 20g butter over a medium heat. Add the flour and cocoa, stirring continuously until combined and starting to thicken. Gradually beat in the hot chocolate milk with a wooden spoon until it forms a very thick, smooth paste. Scrape into a mixing bowl; cool for 5 minutes.
4 In a clean bowl, whisk the egg white to medium peaks. Whisk in the remaining 20g sugar, 1-2 tbsp at a time, until glossy. Beat the yolk into the chocolate mixture.
5 Use a metal spoon to mix a spoonful of the egg white into the chocolate mixture to loosen, then gently fold in the rest. Spoon into the ramekins, filling them to 2cm below the rim. Bake on the tray for 14-15 minutes, until risen with a slight wobble in the middle.
6 Meanwhile, whip the double cream with the icing sugar and vanilla to soft peaks; fold in the crème fraîche. Dust the soufflés with icing sugar and serve at once with the cream. (They will sink within a few minutes.)