Sea Urchin and Crab Fondue

Name: Sea Urchin and Crab Fondue
Ingredients: 4 (6-ounce) Y ukon Gold potatoes; 3/4 teaspoon kosher salt plus more to taste; 3/4 cup heavy cream; 10 tablespoons cold unsalted butter , cubed; 1/4 teaspoon black pepper; 3/4 cup water; 1/2 cup plus 1 tablespoon unsalted butter , softened and cut into pieces, divided; 2 medium shallots , finely chopped (about 1/2 cup); 1/4 cup dry white wine; 8 ounces fresh jumbo lump crabmeat , drained and picked over; 3 tablespoons finely chopped fresh chives , plus more for garnish; 2 teaspoons fresh lemon juice , plus more to taste; 1/2 teaspoon kosher salt , plus more to taste; 1/8 teaspoon black pepper; 12 sea urchin tongues (about 4 1/2 ounces)