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Ingredients
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    A little vegetable oil for greasing

    175g plain chocolate, broken into pieces, plus extra for decoration

    15g unsalted butter, chopped

    4 large free-range eggs, separated 175g caster sugar, plus extra for decorating

    Grated zest and juice of 2 lemons, plus 2 lemons for decorating

    12g sachet powdered gelatine

    300ml double cream


    AND THIS IS WHAT YOU DO......

    1.  Grease a 20cm loose-bottomed springform cake tin, line the base and sides with baking paper, then grease again. Put the chocolate and butter in a heatproof bowl over a pan of barely simmering water (don’t let the water touch the bowl). Melt.

    2.  Pour the chocolate into the cake tin and spread all over the base and sides with a rubber spatula or pastry brush – the sides should look a bit rough and jagged. Chill until firm.

    3.  In a bowl, whisk the yolks, sugar and zest for 5 minutes until pale and thick. Put the lemon juice and 2 tbsp cold water in a small pan, bring to a boil, then remove from the heat and sprinkle the gelatine evenly over the surface. Stir until dissolved.

    4.  Pour the hot gelatine liquid over the egg mixture, whisking until thick.

    5.  In 2 bowls, using clean beaters, whisk the egg whites, then the cream to soft peaks. Fold the cream, then the whites into the egg mixture with a big metal spoon. Pour into the cake tin, making sure the soufflé comes below the top of the chocolate. Wrap the tin in cling film and freeze for at least 3 hours until firm.

    6.  Meanwhile, make the decorations. Slice the lemons into fine rings (discard the ends). Coat in sugar, then caramelise in a hot, dry pan until golden brown on both sides. Leave to cool completely.

    7.  About 20 minutes before serving, remove the soufflé from the freezer. Peel away the cling film and rub the outside of the tin with a hot cloth. Unclip and carefully remove the tin’s sides. Peel the baking paper from the base and sides, decorate the top with the lemon, then transfer to a serving platter or cake stand. Serve very cold but not completely frozen.