When making the creme patissiere for the Gooey Chocolate Stack I would like to substitute cornflour for the flour to make it gluten free. Can you tell me how much I should use?
Nigella's Gooey Chocolate Stack (from HOW TO BE A DOMESTIC GODDESS) is made with layers of chocolate flavoured meringue sandwiched with a chocolate creme patissiere. The creme patissiere is a chocolate custard thickened with flour and egg yolks. The chocolate added to the mixture will also help it to thicken.
Usually if you need to substitute flour with cornflour (cornstarch) for thickening a sauce then you need to use half the quantity of cornflour. However in this particular recipe the amount of flour used is quite small relative to the amount of liquid and so we think that in this case it may be best to use the same amount (2 tablespoons) of cornflour. For sandwiching the meringue layers we feel that it is better to err on the side of a slightly thicker creme patissiere rather than one that is too thin.