Preheat the oven to 180C/160C Fan/Gas 4. Grease and line a shallow 18cm/7in square cake tin and line the base with baking parchment.
For the genoise, gently melt the butter in a pan, then set to one side to cool slightly. Measure the eggs and sugar into a large bowl and whisk at full speed until the mixture is pale, mousse-like and thick enough to leave a trail when the whisk is lifted from the mixture.
Sift the flours together into a bowl. Carefully fold half the flour into the egg mixture, then gently pour half the cooled butter around the edge of the mixture and fold in. Repeat with the remaining flour and butter. Pour the mixture into the prepared tin.
Bake for 35-40 minutes until well risen and the top of the cake springs back when lightly pressed with a finger. Leave to cool in the tin for a few minutes then turn out, peel off the parchment and finish cooling on a wire rack.
To make the coffee icing, measure the butter into a small pan and gently heat until the butter is melted. Remove from the heat and stir in the coffee powder until dissolved. Add the icing sugar and beat until smooth and glossy. Set aside to thicken.
For the crème au beurre moka, measure the sugar and 2 tablespoons water into a small heavy-based pan. Heat very gently until the sugar has dissolved. Bring to the boil then boil steadily for 2-3 minutes or until the syrup is clear and forms a slim thread when pulled apart between 2 teaspoons. (CAUTION: melted sugar is very hot. Take care not to burn yourself).
Put the egg yolks into a small bowl and give them a quick whisk to break them up. Add the syrup in a thin stream over the yolks, whisking all the time until all the syrup is incorporated and the mixture is thick and cold (it’s easiest to do this in a freestanding mixer).
In another bowl, cream the butter until very soft and gradually beat in the egg yolk mixture. Stir in the coffee essence to flavour. Spoon into a piping bag fitted with a number 7 star nozzle.
To assemble, cut the cold cake in half horizontally and sandwich the slices together with the coffee icing. Trim the edges and cut the cake into 9 equal squares.
Heat the apricot jam in a pan, then pass through a sieve into a small bowl. Brush the sides of the cakes with apricot jam and press the chopped almonds around the sides.
Pipe tiny rosettes of crème au beurre moka very close together around the top edge of the cakes (they should create a solid outline that can be filled with icing). Pipe tiny rosettes of crème au beurre moka around bottom edge of the cakes.
For the fondant icing, knead the fondant icing until soft (if it’s really hard heat it in a microwave for a few seconds). Beat with a wooden spoon until smooth (alternatively you can do this in a food processor). Gradually beat in 4 tablespoons water and enough food colouring to make a coffee coloured glaze. Carefully spoon the glaze into the centre of the top of the cakes and leave to set.