I've been reading around a bit on this style and it seems just Pilsner malt in a traditional Kolsch type beer. If any specialty malt keep below 5% Vienna and wheat may be used. Low hops .40 - .6 bu/gu. Ferment cool to keep the esters and fruitiness low some sulphur is ok as well as fruitiness but keep it to a minimum. Larger near freezing for at least a month to help clear it up. That's what I sourced from round the brew forums.
I'm with you there JA a decoction wouldn't hurt especially if just using a single Pilsner base malt to give extra body.