1 Cover three baking sheets with silicone paper. With a lightly buttered finger, trace the outline of an 18cm circle (or thereabouts) on each tray.
2 Gently warm the egg whites and the mixing bowl over a pan of very lightly simmering water, (though take care the bowl doesn't come into contact with the water, otherwise the egg whites will cook) then using an electric whisk, beat the whites to a stiff froth.
3 Sprinkle a quarter of the caster sugar at a time over the whites and whisk through on high speed until the grains disappear and the mixture ends up very thick and glossy. Sift and fold in the icing sugar until the mixture is smooth, then dollop a third of the meringue mix on to each prepared paper circle and spread into a disc shape with a spatula.
4 On Fan Plus bake at 130°C for about 90 minutes, or until crisp, slightly beige coloured and with a firm crust. Remove and set aside to cool.
5 In a bowl, beat the chestnut purée, 250ml double cream, ricotta, vanilla and enough sugar gently to sweeten it, until very thick. Peel one cold meringue from the paper and place on a serving plate. Spread with a third of the chestnut cream and swirl melted chocolate all over. Repeat with a second meringue, chestnut cream and chocolate, and top with the last meringue.
6 Whip 100ml cream until thick. Spoon onto the meringue top to make a peak, then swirl the last of the chestnut cream on top. Drizzle with melted chocolate and serve.
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