Heat the oven to 160 C / Gas 3. Grease and line a 23cm square cake tin.
Put chocolate in a heatproof bowl and place over a pan of gently simmering water. Once the chocolate is melted, stir in the butter. Remove from the heat and let cool slightly.
Beat together the eggs and sugar until slightly thickened. Sift the flour over the mixture and then add the almonds and chocolate mixture and fold in until evenly combined. Turn the mixture into prepared tin.
Bake in preheated oven for about 35 minutes, until just firm. Transfer to a wire rack to cool.
Meanwhile, make the chocolate cream. Heat the cream in a saucepan until almost boiling. Remove the pan from the heat and add the chocolate. Leave until the chocolate has melted, then stir until smooth. Transfer to bowl and leave to cool until thickened.
Slice off the top of the cake if it has risen in the centre. Halve the cake horizontally and sandwich the halves with one-third of the chocolate cream. Spread the remainder over the top and sides of the cake.