So in my few weeks building lather I've tried about every tip on here and on youtube and narrowed it down to this ..
First I have 2 bowls, pottery style I bought them from the thrift store for a dollar and they have been working great go have a look and try to find two sizes so the one can fit well in the other. I also have the bowl I whip my lather in was unglazed pat I think it might help it to hold heat better but that's just imo.
So 1st if you got time put a tea pot on the stove to boil
2nd fill sink with hot tap water put mixing bowl and brush in water
3rd drip a thin layer of the hot water on the puck of soap and then put brush back in sink
4th hop in and out of shower depending on how long you took your water pot should be boiling
5th fill your bigger bowl 3/4 full boiling water. After dumping water from sink out of mixer set it into hot bowl
6th AND I really think this helps ! Pour the thin layer of soap water off puck into mixer bowl
7 I dip the tips of my brush into the Hot stove water, get your brush nice and soapy on your puck and start beating to get a real hot lather

I really like using the double boiler method, and it'd pretty sweet if u just start it b4 your shower your not waiting 4 water to boil. If you can't you can always just use hot tap water and follow other steps, and keep mixer in sink with some hot water to keep it warm !

Good luck. Just beat that stuff till its like whipcream or barbasal then u know its ready.