3/4 cup granulated sugar, ground to a powder in the food processor or blender
To make the pineapple ice: Halve the pineapple lengthwise. With a grapefruit knife (or other small sharp knife), cut around the inside edges and remove the pulp, leaving 1/4-inch-thick shells. Pat the shells dry and freeze them, covered with plastic wrap. Core the pineapple pulp and cut it into 1-inch pieces. In the food processor or in a blender puree the pulp until smooth, blend in the granulated sugar and lemon juice to taste, and transfer the mixture to the ice-cube trays. Freeze the ice in the freezing compartment of the refrigerator until frozen, transfer the cubes to the food processor, and blend them until the ice is light and fluffy. Pack the ice into the pineapple shells, mounding it slightly, and freeze the shells, covered with plastic wrap, in the freezing compartment of the refrigerator until the ice is frozen. Preheat the broiler.
In a bowl with the mixer beat the whites with the salt until foamy, add the cream of tartar, and beat the whites until they hold soft peaks. Add the pulverized granulated sugar, 1 tablespoon at a time, and beat the meringue until it holds stiff peaks.
Transfer the meringue to the pastry bag (fitted with a small star tip) and pipe it decoratively over the ice, covering the ice completely. Sift the confectioners' sugar over the meringue, arrange the shells on a baking sheet, and put them under the broiler about 6 inches from the heat for 30 seconds to 1 minute, or until the meringue is browned lightly. Serve the desserts immediately.