The 32-year-old blitzed his way to the big final in Spain where he came from behind to defeat fellow Austrian Siegfried Grabner and get his hands back on the World Cup title with a round to spare.
Swiss snowboarder Philipp Schoch prevented it from being an Austrian clean sweep though as he beat Benjamin Karl in the small final for third place and his best finish of the season so far.
With one more round left in Sierra Nevada, Prommegger cannot now be caught at the top of the parallel giant slalom World Cup standings with his lead at the top 1380 points.
Roland Fischnaller, who placed ninth in La Molina, occupies second place with 2280 points while Rok Marguc is third in the overall standings another 180 adrift of the Italian.
But, while the men's title is wrapped up, the ladies' is set to go down to the wire after Anke Karstens of Germany came out on top in the big final over another Austrian Marion Kreiner.
Patrizia Kummer, last year's World Cup champion, won the small final ahead of Japan's Tomoka Takeuchi with 202 points separating the top three in the overall standings.
Kreiner leads with 2512 points before Kummer in second with 2480 and then Takeuchi in third with 2310 with the champion to be decided in Sierra Nevada next week.