Tart chocolate porter/stout recipe help

I woke up this morning with a dream of trying a beer in a brewery. What I liked about the beer was a rounded tartness that followed a rich chocolaty-bready-malt-forward and ends with dried fruit esters and a lasting chocolate flavor.

I've been obsessed with lighter-bodied sours and farmhouse ales for the last couple years now. They were the styles I couldn't afford in bars but wanted a supply of. But I'm looking to expand my horizons a bit. The beer I had in my dream was a cask-aged chocolate porter or stout. The brewing school I'm attending in Washington just got three barrels from the local wine industry and I'm free to utilize one. There is no rush in filling a barrel so I'm looking to make two or three iterations of the brew before aging on the oak and then I will have a baseline to compare it to.

One concern I have is the chocolate aromatics dissipating over time. This may be rectifiable by adding nibs at the end of its conditioning (be it fermenter or barrel).

Another concern is the tartness, do I put the beer on fruit for malic acid, do I introduce some pedio, do I simply make a very short kettle sour (12-24 hours) just to add a slight sharpness on the palette before the chocolate takes over?

The grain bill I first sketched is as follows:

Maris Otter ~40%
Vienna ~25%
Munich 20L ~10%
Wheat ~4%
Flaked Oat ~6%
Carafa I ~4%
Black Malt ~1%

Brown Sugar ~7%

Thanks to Greg's recipe I'm tweaking: http://www.maltosefalcons.com/tech/formulating-and-brewing-winning-chocolate-porter

Suggestions?

Looks pretty good. Good luck literally brewing the beer of your dreams.

What type,of, tart? Like sour cherry? I've made a sour,black,tripel that has a definite cherry afterflavor. The sour tartness is what will linger on your palate though. Not the chocolate.

The Yeast election for this will,play a major role. Are you planning on using cacao nibs? Is definitely,go that route.

Definitely nibs, forgot to put that in. Im thinking nibs and vanilla bean in vodka extract in secondary. Good question as far as tartness, i want something subtle so maybe putting it on fruit for malic acid instead of letting bugs do any work. Id prefer something more chocolate than sharp if i have to choose.