1. Preheat oven to 450°.
2. To prepare pastry, place first 3 ingredients in a food processor; pulse to combine. Add butter; pulse 10 times or until mixture resembles coarse meal. With processor on, slowly add 2 tablespoons ice water through food chute, processing just until dough starts to come together. Turn dough out onto a piece of plastic wrap; press into a disk. Cover and chill 10 minutes in the freezer. Place dough between 2 sheets of plastic wrap; roll dough into a 10-inch circle. Fit dough into a 9-inch round removable-bottom tart pan coated with cooking spray; pierce dough with a fork. Bake at 450° for 10 minutes or until lightly browned. Cool completely on a wire rack.
3. To prepare pastry cream, combine brown sugar, 3 tablespoons flour, and 1/8 teaspoon salt in a medium, heavy saucepan. Gradually add milk, stirring with a whisk. Scrape seeds from vanilla bean; add seeds and bean to milk mixture. Cook over medium-high heat until thick and bubbly (about 5 minutes), stirring constantly. Place egg in a large bowl. Gradually stir hot milk mixture into egg. Return milk mixture to pan; cook 2 minutes or until mixture reaches 185° and coats the back of a spoon, stirring constantly. Discard vanilla bean. Spread pastry cream onto a baking sheet; cover entire surface with plastic wrap. Refrigerate 20 minutes or until chilled. Spread pastry cream evenly into tart shell; cover and chill at least 2 hours or until set.
4. To prepare topping, combine juice, cinnamon, nutmeg, and pears; toss well to coat. Place pears, cut side down, in an 11 x 7–inch baking dish coated with cooking spray. Bake at 450° for 45 minutes or until tender. Cool completely; thinly slice. Place on paper towels; pat dry with additional paper towels. Arrange the pear slices spoke-like over pastry cream. Cover and chill at least 30 minutes.
5. Sprinkle 1/3 cup granulated sugar evenly over pears, leaving a 1/2-inch border. Holding a kitchen blowtorch about 2 inches from the top of custard, heat the sugar, moving the torch back and forth, until the sugar is melted and caramelized (about 3 minutes). Serve immediately.