Step-mashing reportedly is unnecessary since modern malt is so well modified. If so, why is it still done? I've never been able to get a Dubbel dry enough even when mashing @146F for 90 minutes. Perhaps it was a pH issue, but then again maybe the step mash would've helped.
Recipe looks decent. I'd given up on brewing the Belgie's but- *sigh* could always try another.
My mash profile for Dubbel's is single step 90min @ 150F, I use RO water with salts added in mash for to get at least 50ppm of Ca and adjust pH. Even with a highly fermentable wort the fermentation profile is where I get the attenuation.
I use mr malty calculator and add additional 20% wort vol (personal pref.) Stir plate for 72hrs (stll playing with total time), chill overnight, decant, and pitch. I have temp control and for WLP530 I pitch at 64F hold for day and then let rise and finish and hold at ~72F letting sit on yeast for at least a week after FG. I get the "dryness" I'm looking for maybe 8 out of nine beers and its always tricky with dark versions.
For me, getting within a pH range 5.3-5.7, 90m boil for pils, and fermentation control have improved my belgians quality. I only brew belgians and they still drive me crazy. Hang in.