Adjust oven rack to center position and preheat oven to 450°F (230°C) or 400°F (200°C) if using convection. Heat 2 quarts (2L) water in a large pot over high heat until boiling. Add 2 tablespoons kosher salt (about 1 ounce; 25g), baking soda1/2 teaspoon, and potatoes4 pounds and stir. Return to a boil, reduce to a simmer, and cook until a knife meets little resistance when inserted into a potato chunk, about 10 minutes after returning to a boil.