Well, my answer depends on what you define as "traditional".
For me, stout is pale malt, roasted barley (maybe some Chocolate malt), and something flaked for body enhancement. Flaked barley = Dry Irish Stout; flaked oats = Oatmeal Stout. Add some crystal malt of some sort, and you're in the newer style territory of American Stout.
I've never brewed a Belgian Stout before, but now you've got me thinking.
I like the idea of taking a tried-and-true recipe and tweaking one bit, in this case the yeast strain. (Read through my posts here and the trend of KISS will become apparent.) Perhaps I'll try that with my American Stout in my recipe dropdown.
I note with some dismay that brewers here talk about using all Belgian ingredients in Belgian-style ales. To the best of my knowledge, commercial Belgian brewers don't use Belgian-grown pils base malt; as a general rule they use "Continental" pils, whatever base malt is least expensive but provides the extract and flavor potential they need, that they can reliably predict. I agree strongly - use the base malt you use all the time, that you know inside and out, and can make work for you. First, the overwhelming majority of people couldn't tell what Pils malt you used. Second, the pro brewers in Belgium don't use Belgian malt. Third, in a beer like this anything "special" a base malt can provide is going to get completely smothered anyway. So why waste the money?
Also, to the best of my knowledge some Belgian Pils malts are undermodified compared with the pale malts with which homebrewers are familiar. Castle's is well modified and suitable for single-infusion mashing, as is Dingeman's, but Franco-Belges has many of the characteristics (which I prefer, if that's important) with the late, lamented DeWolf-Cosyns Pils malt, including the low protein content, less modification and lesser friability than other pils or pale malts.
Specialty malts, yes, by all means use Belgian if you can. Special B is of course the
de rigeur Belgian crystal malt.
Castle produce a Black Malt which, while not a direct substitute for English or American roasted barley - because it's closer to Black Patent than RB - can be subbed to an extent. I <3 Castle's
Chocolat malt. But for the base malt I'd use whatever I use the most and am most familiar with, in order to get closer to assuring success.
I don't know I'd use sugar here. In order to get a noticeable flavor contribution, you'd simply have to use too much dark candisugar; what you can notice in a Dubbel brewed traditionally - Pils malt and dark candisugar - you sure as hell won't notice in stout! And that's the max I'd use in terms of sugar, ~20% of the grist.
I concur with one hops addition for bittering only. Let the yeast's flavors play with the roasty and caramel/fruit flavors of the malt.
I'm playing in BrewTarget in another window.
Cheers!
Bob