The lexical verb molten is unusual and appears to be archaic; it is not listed in the Oxford English Dictionary. Nonetheless, it is not an error here in Ether 3:1 since the word is used four other places in the Book of Mormon text; in each case, the meaning is ‘to cast (metal)’:
The critical text of the Book of Mormon will maintain all five instances of the archaic lexical verb molten.
The OED recognizes the word molten as a past-participial adjective form that is historically derived from the past participle of the lexical verb melt. We can find one instance of this adjectival use of molten in the Book of Mormon, namely, in a biblical quote from the King James Bible:
There is also an instance in the King James Bible of the past-participial form molten being used in the perfect for the transitive verb melt:
This is equivalent to “who hath molten a graven image”. Modern translations (such as the Revised Standard Version and the New International Version) translate this passage with the lexical verb cast.
Summary: Maintain the archaic lexical verb molten, which means ‘to cast (metal)’; this verb occurs five times in the Book of Mormon text (twice in 1 Nephi 17 and three times in Ether).