Mash grains with 15 qts. (14.2 L) soft water at 142 °F (61 °C) and hold for 30 minutes. Perform a decoction, pull 1/3 thick portion of the mash (~1.5 gallons/5.7 L) and bringing to a boil. Boil for 15 minutes being sure not to scorch the grain mix. Stir the decocted portion back into the main mash. The main mash should now settle at 155 °F (68 °C). Hold for a 30 minute rest. Mash out, vorlauf, and then sparge at 170 °F (77 °C) to collect enough wort to result in 5 gallons (19 L) after a 90-minute boil. Boil 90 minutes, adding hops at times indicated. Cool, aerate, and pitch yeast. Ferment at 50 °F (10 °C) until signs of fermentation have slowed considerably. Some diacetyl is noted in Pilsner Urqell, but if there is a strong diacetyl presence at this point, 2-4 days at 65 °F (18 °C) is advised. Rack to secondary and lager for 4-6 weeks at 40 °F (4 °C). After lagering is complete, bottle or keg as usual.