Blackberry and bramley layer cake

Preheat the oven to 180 degrees C, gas mark 4. Grease and line the bases of 3 x 20cm round sandwich tins. Put all the sponge ingredients into a large bowl and use electric beaters to mix until smooth. Add more milk if needed to reach a soft dropping consistency. Spoon into the tins, spread evenly then bake for 28-30 minutes, until risen and golden. Cool in the tins for 10 minutes, then turn out, top-sides down, to cool completely on a wire rack (this will help keep the cakes flat).

Meanwhile, make the filling. Put the blackberries into a medium pan with 2 tbsp sugar and 2 tsp lemon juice. Bring to a simmer; cover and cook over a low-medium heat for about 5 minutes, until the fruit has collapsed into its juices. Mash well, then set aside.

Chop the apple and put in another pan with the remaining 2 tbsp sugar and 2 tsp lemon juice, plus 1 tbsp water. Cover and cook over a medium heat for 5-7 minutes until soft. Mash into a purée, then stir in the blackberry coulis; set aside to cool.

For the frosting, put the egg whites, icing sugar and a pinch of salt in a large bowl over a pan of simmering water, ensuring the water does not touch the base. Use electric beaters to whisk until thick and stiff (5-7 minutes). Spoon into a cold bowl and continue to whisk until the mixture is cool (about 5 minutes). Whisk in the butter, 1 tbsp at a time, until all incorporated and silky. Beat in the cinnamon, then chill for 30 minutes.

Put 1 sponge onto a serving plate or cake stand and spread with one third of the buttercream, then spread over ½ the apple and blackberry mixture; repeat. Top with the final sponge and spread ¾ of the remaining buttercream on top. Use the final ¼ of buttercream to thinly coat the sides, allowing the berry filling to catch in it, creating a ripple effect. Top with the remaining blackberries and the lemon zest strands.