Heat oven to 375ºF
Grease an 8 ½ (22cm) springform cake tin with soft butter and line the bottom with baking parchment.
Shake a little flour around the buttered edges.
Melt the chocolate and butter together over a pan of simmering water, or in a microwave.
Whisk the eggs with the brown sugar and caster sugar, either in an electric mixer or with an electric hand whisk, for 5-10 mins until thick and pale.
Pour the chocolate mixture onto the beaten eggs and sugar, and gently mix until smooth.
Add the almonds (if using) and flour and mix again.
Pour the batter into the prepared tin and bake for 35-40 mins until the cake is set but with a slight jiggle in the centre.
(If the cake is starting to brown too quickly, cover with a piece of aluminum foil)
Leave to cool in the tin – it will sink a little as it cools.
Run a knife around the inside of the cake tin to loosen.
Remove the baking parchment and place on a cake stand.