Combine 5 ounces kosher salt (1 cup Diamond Crystal or 1/2 cup Morton), 1/4 cup sugar, and 1 teaspoon black peppercorns in a large pot. Squeeze in juice from 1 halved lemon and add lemon to pot along with 2 quarts water. Bring to a boil, stirring to dissolve salt and sugar. Remove pot from heat and stir in 2 quarts ice water. Add one or two 2 1/2-pound chickens to brine, weight with a plate to keep submerged, if needed, and cover. Chill 12–24 hours.