Took me awhile to figure out you wanted I needed to search for Sebastiaan.
Sadly there isn’t much info: “A single batch of St. Sebastiaan Grand Réserve is brewed each year. This limited edition release from Brewery Sterkens is brewed with utmost care to be one of the finest beers in the world.”
Consider brewing a big triple or strong golden, then tweaking from there to get it closer.
Sorry I couldn’t give you more help.