Step 1Scrub potatoes beneath cold running water and pat dry with paper towels. Pierce each potato several times with fork. Bake at 425 degrees until potatoes are fork tender, about 1 hour.
Step 2While potatoes bake, saute cabbage and leeks in skillet coated with nonstick cooking spray over medium heat until vegetables begin to wilt, about 2 minutes. Add chicken broth. Cover and steam until cabbage turns bright green and tender, about 10 minutes. Season with 1/2 teaspoon salt.
Step 3Remove potatoes from oven and cut horizontal slice off top third of each potato. Scoop pulp from potatoes into bowl, leaving shells about 1/4-inch thick. Scoop pulp from tops of potatoes and add to bowl. Process potato pulp through potato ricer. Stir in milk. Add cabbage and leeks. Season to taste with salt and pepper.
Step 4Spoon potato mixture into 4 shells, dividing evenly. Brush tops of potatoes with melted butter, then sprinkle with dash paprika and bake at 425 degrees until tops are lightly browned, 20 to 25 minutes. Garnish with chives.