Combine melted butter, sour cream, egg, vanilla, salt and remaining sugar in large bowl. Beat until well blended. Add 1 cup flour; on low speed, beat until well mixed. Add yeast mixture and 1 more cup flour; beat 2 minutes at medium speed, scraping down side of bowl occasionally. Gradually stir in remaining 1 cup flour to make medium-soft dough (dough should be softer than bread dough).