Why Didn't My Flourless Peanut Butter Cookies Flatten When They Baked?

Our answer

NIgella's Flourless Peanut Butter Cookies (from SIMPLY NIGELLA) are made with very few ingredients and there are a few reasons why the cookies may not have spread. The leavening agent is bicarbonate of soda (baking soda) and for cookies the effect is to make the cookies spread out as they bake. If the bicarbonate of soda was old or incorrectly stored, or too little was used, then it may not have been as active.

If the cookie dough is cold then this can also affect how the cookies bake as it will take longer for the fats in the cookie dough to melt. If you are baking the cookies from chilled or frozen then you need to increase the baking time slightly (see the Additional Information box below the recipe). Finally, if the cookies are very dark on the bottom then this is usually an indication that the oven is a little too hot and the outside of the cookie will set before they can spread. This is less common in flourless cookies but could be an indication that the oven is slightly too hot, as all ovens vary, and you may need to reduce the temperature slightly.