Do you know about Ron Pattinson? He is a beer historian who researches brew log books from long gone London/UK breweries and translates the recipes to homebrew scale. If you are more interested in modern Porter then his info is probably not for you but if taking a look at recipes from the origins and heyday of Porter (once the most popular beer in the world with London breweries being the largest producers in the world) then check out his blog and search for Porter.
https://barclayperkins.blogspot.com/search?q=Let's+Brew+Porter
He also has books available. One of the best for its concentration of both info and recipes is The Homebrewers Guide to Vintage Beer.
I have collected a few hundred of his recipes and one of the best Porter recipes comes from the Whitbread Brewery in London and comes from their 1880 logbooks. Historical recipes are dead simple and contain only a handful of malts. There were three that cropped up in nearly every Porter recipe that Ron dubs the London Trinity... Pale, Brown and Black.
I posted this one in the recipe database about five years ago. Here is the gist of it...
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Recipe Type All Grain
Yeast English Ale (Whitelabs #WLP002)
Yeast Starter 1.0 Liter
Batch Size (Gallons) 6
Original Gravity 1.053
Final Gravity 1.010
Boiling Time (Minutes) 60
IBU 34.4
Color 34 SRM
Primary Fermentation (# of Days & Temp) 14 Days. 66F until day 12 when raised to 72F
Secondary Fermentation (# of Days & Temp) none
Tasting Notes Roast and chocolate notes. Malt forward but only slightly sweet. Only a hint of hop bitterness. Silky smooth finish.
9 lbs Pale Malt
1 lb 12 oz Brown Malt
12 oz Black Malt (not patent)
2 oz East Kent Goldings (6.4%) boil 60 minutes
1 Liter starter using WLP002 English Ale Yeast
Mashed at 152 for 60 minutes.
My intent was to brew a traditional, English Porter as a starting point to build up a modern, robust porter. However upon first taste I don't think I want to change this recipe much if any. The recipe is one of Ron Pattinson's historic recreations based on Whitbread brewing logs.