This cake rises spectacularly in the oven and sinks a little as it cools,
resulting in a fractured, sugary crust. The recipe makes just the right amount
of batter for a 22cm-diameter tin.
Serves 8
150g dark chocolate
125g salted butter, cubed
Zest of 3 limes
3 large eggs, separated
200g caster sugar
70g plain flour
1 Preheat the oven to 170C/335F/gas mark 3 . Grease and line the cake tin,
preferably a loose-bottomed one.
2 Gently melt the chocolate either in short bursts in the microwave or in a
bowl over a pan of simmering water (don t let the bowl touch the water).
3 Stir the butter and zest into the chocolate, heating for a short while longer
if necessary, until the butter is melted. Set aside to cool a little.
4 Whisk together the egg yolks with 100g caster sugar until thick, creamy and
far paler in colour. It s the right consistency when the mixture falling from
the whisk leaves a ribbon on the surface of the mix. Make sure you whisk the
yolks and sugar together promptly if the sugar just sits on top the yolks it
will cook the egg, resulting in rubbery bits of yolk.
5 In a clean, dry bowl, with an equally clean, dry whisk, beat the egg whites
until completely foamy. Continue to whisk, adding the remaining 100g sugar one
tablespoon at a time. Whisk well between each addition of sugar. The mixture
will become thicker and glossier until slowly lifting the whisk out of the
mixture leaves a soft peak a tapering curl of meringue, slightly droopy at
its tip.
6 Fold the egg yolk mixture into the chocolate. Now fold a third of this
chocolatey mixture into the whites. As soon as this is basically combined but
still marbled, add the next third, and so on. Sift in half the flour. Gently
fold until nearly combined, then sift in the remaining flour and fold until
just homogenous. The most important thing here is to keep as much air as
possible in the batter gently cut through with the spoon, don t beat it and
mix only until just combined.
7 Spoon the batter into the prepared cake tin and bake for 30-35 minutes. Let
it cool in its tin before releasing.