I have made Nigella's Lemon Polenta Cake twice and have found that it rises beautifully but once I take it out of the oven, before pouring over the syrup, the cake falls down significantly in the center. I would love to know how to rectify this as the cake is super delicious and an absolute favourite of my family. Look forward to hearing from you!!
Nigella's Lemon Polenta Cake (from Kitchen and on the Nigella website) is a flourless cake made with ground almonds (almond meal) and fine polenta. This means that the cake is gluten free. Unfortunately gluten free cakes can tend to sink in the centre as they cool and so this is quite normal. If you look carefully at the photo with the recipe you will see that the cake in the photo has also sunk a bit in the centre.
Gluten is a protien found in flour and it can form a strong structure when it is exposed to liquid and heat. In a cake made with wheat flour the gluten strands form as the cake is mixed and then set in the heat of the oven. As it sets it traps the carbon dioxide bubbles (from the baking powder) in the cake's structure and the cake keeps its shape as it cools. Unfortunately for gluten free cakes there is no gluten to set so as the carbon dioxide bubbles in the cake cool and shrink, the cake will start to shrink back too. You may find that baking the cake for slightly longer will slighty reduce the sinking, but it will not eliminate it completely. Also watch that the edges of the cake don't burn if you bake it for slightly longer.