Mixing Walnuts Into Coffee And Walnut Layer Cake

Our answer

Nigella's Coffee And Walnut Layer Cake (from KITCHEN) is a sponge layer cake that includes ground walnuts. If using the food processor method, the nuts should be ground with the sugar at the beginning of the recipe and not added at the end. But from the description, we assume that the cake is being made without a food processor and the walnuts are being crushed to a fine rubble, rather than being blitzed to a powder.

It could be that the oil released from the walnuts as you crush them is just enough to cause curdling, though as the flour usually stabilises the cake batter it is slightly unusual for it to happen right at the end. But we would highlight that a non-food processor method is given where the crushed walnuts are mixed with the dry ingredients (the flour, baking powder, bicarbonate of soda (baking soda) and espresso powder) and then this dry mixture is added to the creamed butter and sugar, alternating with the eggs. If you click on the recipe link above, you will see this method in step 5. This is a slightly safer way of adding the walnuts, as any oil released will be absorbed by the flour before the walnuts are mixed into the cake batter. We would also suggest that you make sure that all of the ingredients, including the milk, are at room temperature, as if ingredients are too cold then this can also cause a cake batter to curdle.