Melt the chocolate in a heatproof bowl set over a pan of simmering water, ensuring the bowl doesn’t touch the water. Alternatively, melt it in short bursts in the microwave, stirring between each burst. Set the chocolate aside to cool a little while you separate the eggs. Whisk the egg whites and a pinch of salt using electric beaters until they form soft peaks, then gradually add 200g of sugar, continuing to whisk until the egg whites form stiff peaks.

Line a 24cm springform tin with baking parchment. Heat the oven to 170 C/150 fan/gas 3. Using electric beaters, beat the butter and remaining sugar in a large bowl until light and creamy and the sugar has dissolved. Gradually beat in the egg yolks and cooled chocolate. Fold about 1/3 the whisked egg whites into the chocolate mixture. Sift the flour over the mixture in two batches and fold each in. Gently fold in the remaining beaten egg whites using a spatula.

Pour the cake batter into the prepared tin, spread evenly and bake for about 1 hr or until the cake is risen and springy to the touch. Put on a wire rack and leave to cool completely in the tin.

Heat the jam and liqueur (or juice) in a small saucepan, then pour into a bowl through a fine sieve. Loosen the bottom of the cake tin, then slide off the tin and peel away the baking parchment. Halve the base horizontally. Place the bottom layer on a cake stand and spread with half of the jam mixture, then place the other half of the cake on top. Spread a thin layer of the remaining jam all over the cake and leave to dry.

For the chocolate glaze, bring 40ml water and sugar to the boil in a small saucepan until the sugar has dissolved. Leave to cool slightly, then stir in 2 tbsp of the double cream. Heat the remaining cream in a separate pan and stir in the butter until melted. Remove from the heat and gradually add the chocolate, letting it melt into the cream, and stir in the sugar syrup. Place the cake on a cooling rack over a tray to catch any excess glaze. Evenly coat the cake with the glaze by pouring it slowly into the middle, tilting the cake gently so it flows slowly over the edges. Don’t smooth it with a knife or it will look streaky. Best enjoyed fresh but will keep for up to three days.

For the striped pattern, melt the milk chocolate either in a microwave or in a heatproof bowl set over a pan of simmering water, ensuring the bowl isn’t touching the water. Pour the melted chocolate into a small piping bag and pipe onto the still-damp icing in parallel strips, 2-3cm apart. Carefully pull the tip of a spoon alternately from top to bottom through the lines to make the pattern, then allow the glaze to dry.