Heat the oven to 180℃/160℃ fan (355℉/320℉).
Add your butter and caster sugar to a large bowl. Beat together until pale and creamy
Add in the eggs, one at a time, beating slowly until fully combined.
Sift in the self-raising flour and add in the lemon zest. Mix until well combined.
Divide the mixture in half between two bowls. Add a few food colouring drops to one of the bowls and mix. Keep adding food colouring until your cake batter is your desired shade of pink.
Line a loaf tin (8 x 21cm) with greaseproof paper. Spoon in the mixture alternating between plain and pink batter. When you've added half of the batter scatter in your raspberries before adding the rest. Swirl a skewer through the batter to create a marble effect.
Bake the cake for 45-50 mins until a skewer inserted into the centre comes out clean.
Mix together the icing sugar, lemon juice and 1½ milk until combined. Remove 1/3 from the bowl and set aside in a small bowl. Keep adding drops of food colouring until your icing is your desired shade of pink.
To the small bowl, add the remaining ½ tbsp of milk and stir to combine.
Remove the cake from the oven. Prick the cake several times with a fork and drizzle over the plain icing.
Leave the cake to cool completely in the tin before removing.
Remove the cake from the tin. Drizzle over the coloured icing and top with the remaining raspberries and lemon zest.
