Preheat the oven to 400 degrees F.
Cut the pineapples in half lengthwise, keeping the greens on top intact. With a knife, hollow out each half, leaving a 1/2-inch shell intact. Cut away and discard the cores. Chop the pulp into 1/2-inch dice, place in a medium bowl, and toss with 4 tablespoons of the rum.
Place the pineapple shells on a baking sheet and bake until dry, 8 to 10 minutes. Remove from the oven and let cool completely.
Add the softened ice cream to the diced rum-soaked pineapple and mix until well incorporated. Place in the freezer to harden slightly. Scoop the ice cream into the center of each pineapple shell. Place on a small baking sheet and freeze until very firm, at least 4 hours or overnight.
Preheat the oven to 450 degrees F.
In a large bowl, beat the egg whites until foamy. Add the cream of tartar and beat until soft peaks form. Beating constantly, gradually add the sugar, and continue to beat until glossy and stiff peaks form. Transfer to a pastry bag.
Remove the pineapple halves from the freezer.
Spread meringue over pineapple, making it at least 1 inch thick and mounding it on top. Make an indentation with a tablespoon in center of meringue deep enough to fit eggshell. Bake meringue until edges are lightly browned, about 5 minutes. Or, brown with blowtorch until lightly browned. Carefully transfer pineapple to a serving plate using 2 metal spatulas and place eggshell in indentation. Pour remaining 2 tablespoons of rum into eggshell and carefully ignite with a kitchen match. Spoon flaming rum evenly over meringue (flaming rum will brown meringue a little more). Remove eggshell and serve baked Alaska immediately.
Yield: 8 servings