Raspberry Swirl Mud Cake

Our answer

Unfortunately we believe that the recipe you are referring to may have been a reader's recipe from the old Nigella website. However if you are marbling or swirling ingredients into a cake batter you need to have two mixtures with fairly similar consistencies and rising qualities, otherwise the denser one (in this case the raspberry puree) will sink down as the cake batter rises in the oven.

To get the swirl to stay in the cake, it would be best to stir some of the cake batter into the raspberry puree - enough so that the puree has a similar consistency to the batter. This may dull the colour of the puree so you could carefully add a couple of drops of red food colour to the raspberry batter to boost the colour and increase the contrasting effect in the finished cake. Spoon the mud cake batter into the prepared cake tin (pan) then drop spoonfuls of the raspberry batter into the tin and swirly gently with a skewer. You should only need a couple of strokes to swirl the batter, if you are too vigorous then the two better will start to mix together.