Now, remove the thermometer and whisk in the baking soda. Quickly. Some people like to sift in the baking soda to make sure it’s evenly distributed. Either way It balloons up fast. Once it does, stop whisking or you’ll deflate it. P.S. You don’t want it to overflow. If it gets close, pour gently and with no hesitation onto your lined baking sheet (I used silpat).