150g good quality plain dark chocolate (70% cocoa)
100g butter, plus a little extra for greasing
1 tsp vanilla extract
100g ground almonds
75g xylitol (can be very sweet, depends on taste)
4 eggs separated
Preheat oven to 180°C/Gas mark 4. Grease a 20cm square baking tin and line the base tin (not necessary if using silicone bakeware).
Melt the chocolate and butter in a heat proof bowl placed over a saucepan of gently simmering water making sure that the bottom of the bowl does not touch the water.
Stir very occasionally until the chocolate and butter have melted and are smooth.
Carefully remove the bowl from the heat.
Leave to cool slightly, and then stir in the vanilla extract.
Add the almonds and xylitol. Mix until well combined.
Lightly beat the egg yolks in a separate bowl, and then stir into the chocolate mixture.
Whisk the egg whites in a large bowl until they form stiff peaks.
Add by gently folding a large spoonful of the egg whites into the chocolate mixture, and then fold in the remainder until completely incorporated.
Spoon the mixture into the prepared tin and bake in the preheated oven for 20-30 minutes or until risen and firm on the top but still slightly gooey in the centre.
Leave to cool in the tin and then cut into 12 pieces.