* This sorbet, based simply on commercially canned pears, can be enhanced with the flavor of eau-de-vie de poire (pear liqueur) or, if preferred, with fresh lemon juice. Pears in heavy syrup make a smooth-textured sorbet; pears in light syrup yield a grainier or icier sorbet.
One day before serving, place cans of pears in coldest part of freezer. Freeze until completely frozen, at least 6 hours. Rinse cans briefly under warm water. Open each can at both ends, leaving bottom of can in place. Push the frozen pears and syrup into a large bowl. Let stand just until softened enough to break frozen mass easily into 3 or 4 pieces, about 15 minutes. Remove to food processor.
Process pear mixture, using repeated on/off motion, until slushy. Add liqueur and lemon juice; process until blended. Spoon into freezer container. Freeze, tightly covered, until sorbet is solid and flavors mellow, at least 3 hours.
Meringues: Butter 2 large baking sheets; dust with flour and shake off excess. Using a 4-inch cardboard template or saucer and the point of a wooden skewer or pick, outline four 4-inch circles, even spaced, on each baking sheet. Set aside.
Heat oven to 200F.
Beat egg whites, cream of tartar, and salt in large bowl on medium speed until stiff but not dry. Beat in 2/3 cup of the sugar, 1 tablespoon at a time, beating thoroughly after each addition; beat in vanilla; then continue to beat until whites are very stiff and shiny. If mixture feels grainy when small amount is rubbed between your two fingers, sugar is not dissolved completely, and mixture must be beaten a little longer. Fold in remaining sugar gently but thoroughly.
Spoon meringue gently into large pastry bag fitted with 1/2-inch fluted tip; fill in traced circles on baking sheets, starting at center of each circle and working to outside edge, in even spiral. When all circles are filled, pipe a standing rim around circumference of each circle.
Bake meringue shells until dry and very pale beige, 2 to 2-1/2 hours. Turn off oven; let meringues stand in oven with door closed 2 hours.
Remove baking sheets to wire racks; let meringues stand 15 minutes; then carefully loosen them with wide flat metal spatula and transfer to wire racks. Let cool completely. Use immediately or store loosely covered at room temperature up to 3 days.
Sauce: Puree raspberries in food processor; press through sieve and discard seeds. Mix sugar and cornstarch in small saucepan; stir in raspberry puree gradually; stir until thoroughly blended. Heat over low heat, stirring constantly, until sauce boils and thickens. Remove from heat. Refrigerate until very cold, at least 2 hours. Stir in lemon juice before serving.
Scoop generous portions of sorbet into meringue shells. Pour raspberry sauce over each serving. Serve immediately.