For steeped grains plus malt extract:
Vital Statistics: OG: 1.050 – 1.070, FG: 1.012 – 1.018, IBUs: 25 – 50, SRM: 22 – 40, ABV: 4.8 – 6.5%
The base malt is usually American two-row or pale ale. The roasted malts - chocolate, black patent, roasted barley, and brown - provide the critical roasted flavor. Black patent and roasted barley can become acrid or too stout-like if the proportions are high. A recommendation is to keep the total percentage of roasted malts no higher than 10%. Crystal malts help to balance the roasted character and compose 5% to 10% of the grist. Oats, wheat malt, and cara-pils are optional malts for mouth-feel and beer head.
The hops are usually American or British varieties. One strategy is high-alpha bittering addition followed by low-alpha aroma varieties like Goldings or Fuggle. Citrusy varieties may be problematic by clashing with roasted flavors. Aim for a BU/GU ratio of .60. Late hopping is permissible, but likely not worth the bother.
The yeast should have a neutral character. American ale varieties are a good choice. Relatively clean British strains that attenuate well may also be used.
Beer-analytics.com American Porter
Strong, G. (2023, March-April). American porter: A robust dark brown ale. Brew Your Own, 22 - 24.
Zainasheff, J. (2012, September). Robust porter: Brown and roasty. Brew Your Own, 19 - 23.