That is smooth - I may have to try your method.Hopefully my picture uploads (I'm new to this). But this is a picture of an hp soap that I made. Sorry for the crappy quality. I took it at night so not good quality lighting. But it's a dog shampoo bar that I made for my sister's dog who's name is zombie (that's why they have Z's lol). I think it looks pretty smooth.
I use lard in a lot of my recipes and full water. No clue how long it would take in a double boiler, but as for the crockpot I make WAY more soap than food in mine, so I use the crockpot for soap (super easy to clean), then when I use it for food I use the liners (also super easy to clean).I've only made like 3 HP batches. I cook mine for several hours - maybe b/c I use lard and full water? Or possibly b/c I use a double boiler and not a crockpot. I am planning on getting a soap-dedicated crockpot soon. And I totally scrape the sides!
I usually end up stick blending mine after about an hour.