The challenge of making lather in a mug that has the soap puck at the bottom is that the soap to water ratio is constantly changing. As you are swishing your brush around making lather, you are constantly brushing against the soap puck, bringing in more soap to the ratio. It can be done, but it takes practice. If your lather doesn't work for you, rinse the lather out and try again - soap is pretty cheap. Shaving cream, on the other hand, can start to get expensive.