Hello! I made the Totally Chocolate Chocolate Chip Cookies but the mixture melted and became very flat and as soon as i put them in the oven, moreover after baking them for 18 minutes and then leaving for 5 minutes they were still soft like a cake. The baked cookies were not holding together, they shattered into pieces. I am new at baking and this made me very sad. I also want to ask that what will happen if I don't put bicarbonate of soda. Waiting for your help so that I can try these again.
Nigella's Totally Chocolate Chocolate Chip Cookies (from Nigella Express and on the Nigella website) are the type of cookie that should be slightly crisp on the outside and soft on the inside. From your description of the cookies spreading there could be a few possible sources of the problem. Firstly if it is a very warm day then the cake batter can become very soft and this increases the chances of the cookie dough melting before the outside can bake to a harder shell. You may want to try shaping the cookies and then refrigerating them on their baking sheet for a couple of hours before baking them. Also cookies can spread too much if the oven is too cool so make sure that it is properly preheated and you may want to check it is running at the correct temperature with an oven thermometer.
It is also possible that the butter and sugar were beaten too much which introduces a lot of air and gives the cookies a more cake-like texture. If you leave out the bicarbonate of soda (baking soda) then the cookies will be flat and will be crisp and possibly a little hard. As we have not tried the cookies without the leavening we would not recommend omitting the bicarbonate of soda.