Peel pears. Using a paring knife slice pears in half lengthwise, and remove cores. Wrap 1 pear half in plastic, and refrigerate. Place the other 3 pear halves in a shallow saucepan. Add pear juice and bring to a simmer. Cook until the fruit is tender and can be pierced with a paring knife, 10 to 15 minutes.
Using a slotted spoon, remove pears from poaching liquid. Transfer to a bowl, and discard the poaching liquid. Let cool.
Place pears in a food processor or blender, and puree until smooth. Transfer to a medium bowl.
Pour cream into a small bowl. Using a whisk, beat until very stiff peaks form, about 2 minutes. Fold the whipped cream into the pear puree.
Spoon the pear cream into the tart shells. Gently shake them to level the tops.
Cut 6 (1/2-inch-square) "pegs" from the reserved pear half. Plant 1 peg in the center of each tart. Refrigerate for 15 minutes, or until set. To caramelize the tarts, sprinkle about 1/2 teaspoon of sugar over the top of each tart, including the pear peg. With a propane torch, keeping the nozzle of the torch about 4 inches from the top of the tart, circle the flame over the top of each tart, until the sugar melts. Sprinkle another 1/2 teaspoon of sugar over each tart, and caramelize the sugar with the torch. Refrigerate tarts for 15 minutes before serving.
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