In a large pot, combine potatoes, 3 tablespoons salt, vinegar, and 2 quarts cold water. Bring to a boil over high heat, then reduce heat to maintain a steady simmer. Cook until potatoes are completely tender and offer little resistance when pierced with a paring knife, about 15 minutes. Strain potatoes and let drain, 1 to 2 minutes. Transfer to medium mixing bowl and set aside.

• 4 russet potatoes (2.2 pounds; 1kg), peeled, halved, and cut into about 1-inch pieces
• 3 tablespoons (27g) plus 1 teaspoon (3g) Diamond Crystal kosher salt, divided; for table salt use half as much by volume or the same weight
• 2 tablespoons (30ml) distilled white vinegar