Seems like, the way I understand porters, black malt is kinda mandatory in contemporary (read: post-1820) recipes. After all, that's what black malt was designed for at the time.
Historic porters require brown (and lots of it), and London porters (be they old or new) require at least a bit of brown.
How much black malt a contemporary porter needs, may be up for debate. I settled on 5% for various reasons.
One is colour: 10% brown malt yields, well, brown beer. Decidedly un-porterish. I could have gone for chocolate or carafa but then I'd need to invent a time machine to introduce those malts to 19th century London and my weekend was busy enough as it was.
Another reason was speculative in nature: how much black malt would an actual 19th century porter brewer have used in initial test batches? My guess would be "a tad much", seeing as how used they were to liberally using brown malt. Granted, that's pure and unadulterated speculation from my part.
Cara-amber...yeah I know. That time machine will need to get built after all.
Brewers Gold is, of course, historically bollocks, but it was the only UK pellet hop I had on hand and it'll give me a comparative foothold next to HomoEccentricus' version which got this ball rolling in the first place.
Pellet hops were important because the original recipe calls for a 90' boil of over 100g of vegetable matter, and a 60' boil for another 100g. Made me wonder if those early porters (and IPAs for that matter) didn't all taste like a boiled grass to some extent. I contacted Ron Pattinson to ask his opinion about this. I'll make sure to follow up with his reply.