From Sierra Nevada's website:
Sierra Nevada Porter
O.G. 13.8P (1.056)
Bitterness: 32 IBUS
Bittering Hops: Aurora
Finishing Hops: Yakima Golding
Malts: Two-row Pale, Munich, Chocolate, Caramel, Black & Carafa
With that said, there's nothing special about SN Porter. It's a basic mid-gravity porter recipe that is fermented with their house yeast strain. A good all-grain approximation would be:
Grist Composition
80% American 2-Row
10% 60L Caramel
5% Chocolate (Thomas Fawcett Pale Chocolate is my new favorite)
5% Black Patent
Wort Volumes
post_boil_kettle_wort_volume = 5.75 U.S. gallons
primary_fermentation_vessel_volume = 5.5 U.S. gallons (the delta between the kettle and primary volumes allows one to leave the break and hops in the kettle)
Grist Calculations
average_ brew_house_extraction_rate = a very conservative 26 points per pound per U.S. gallon (~72%)
total_desired_gravity_points = 5.75 x (1.056 - 1) x 1,000 = 332
pounds_of_grist = 332 / 26 ~= 12.77 (we will round down to 12.75 pounds for this example)
pounds_of_2_row = 12.75 x 0.8 = 10.25 (rounded up to the next quarter pound)
pounds_of_crystal = 12.75 x 0.1 = 1.25 (rounded down to the next quarte pound)
ounces_of_chocolate_malt = 12.75 X 0.05 = 10
ounces_of_black_malt = 12.75 X 0.05 = 10
Hopping Schedule (60 minute boil after the hot break)
Kettle: An ounce of any 7-9% AA Northern Brewer derivative at the beggining of the boil
Flavor: 1/2 ounce of U.S. Goldings 15 minutes before knockout
Aroma: 1/2 ounce of U.S. Goldings at knockout.
Yeast: Cultured Sierra Nevada Ale Yeast, Wyeast 1056, White Labs WLP001, or Fermentis Safale US-05