Hi! I regularly make and love Nigella's brownie recipe from 'How To Be A Domestic Goddess'. I've been making it for years now with many variations, but every so often something strange happens. All appears normal, but when baking a lot of the butter seems to separate from the mixture and bubble up. This completely changes the texture of the brownie, making them dry, and they don't get that lovely dense quality with the flaky layer on top. I have tried to pin point what I've done differently, but I can never put my finger on it. There seems to be no explanation for this - please help!
Nigella's Chocolate Brownie Recipe from HOW TO BE A DOMESTIC GODDESS starts by melting the chocolate and butter together in a heavy-based saucepan. We suspect, from the description of the problem, that this mixture is sometimes being overheated and this can cause the chocolate to split. So the fat seeping out is actually cocoa butter rather than regular butter. The remaining cocoa solids then start to cling together which will then give a harder texture to the brownies.
Melt the chocolate and butter together over a very low heat, stirring regularly. It also helps to chop the chocolate finely so that it melts evenly and to remove the pan from the heat before all of the chocolate has melted. Let the pan stand off the heat for a minute or two before stirring until the chocolate has melted. You could also melt the chocolate and butter together in a heatproof bowl over, but not in, a saucepan of hot water. This is a more gentle way of melting the chocolate and reduces the risk of overheating.