This is amazingly only a 15 second exposure, I know you asked for longer but the effect mimics a 1-2 minute long exposure. Taken in Rocky Mountain National Park, CO. The main peak that is being obscured by clouds is Long's Peak. I had planned to use a 15 stop filter or stack others for more but the clouds were moving extremely fast at sunrise so I only needed the 10 stop filter.
The clouds were generic puffy and not totally interesting but because of how quick they were moving, they sort of resemble some lenticular shapes. Hope you like it, or better yet, share your opinion on how it could be better! Cheers, Erik