Manual blend of 2 exposures. The long exposure is made possible by the use of a ND400 filter. I have shot many variations of this composition before. Those mountains are just wonderful when light hits them.
I used a solid ND filter, not a graduated one. The sky was way too bright and the whites clipped for the shot exposed for the foreground. I had to under-expose another shot to get detail in the clouds. I then blended the 2 together.