FOR DOUGH: In a large bowl whisk together flour, confectioners sugar, Demerara sugar, corn starch and salt.

Add butter, egg yolks, cream and zest, then mix together until dough resembles coarse meal. Knead until smooth, sticky dough forms, then flatten into a disc and wrap in plastic. Chill for at least 1 hour or overnight.

FOR CARAMEL PASTRY CREAM: Line a baking sheet with parchment paper. In a medium skillet, stir together 1/4 cup sugar and 2 tablespoons water over low heat until sugar is dissolved, about 2 minutes. Increase heat to medium-high and cook until sugar becomes a deep brown color, about 7 minutes. Pour mixture onto prepared baking sheet and let cool completely, then break caramel into small pieces. Set aside.

In a bowl, vigorously whisk together egg yolks and remaining 1/4 cup sugar until thick and pale, about 2 minutes. Add
flour and whisk until smooth.

In a medium saucepan, bring milk and vanilla just to a boil over medium heat, then remove from heat.

In a slow and steady stream, whisking constantly, add about 2 tablespoons hot milk to egg mixture, then, whisking, add remaining milk. Pour mixture back into saucepan, return to medium heat and, whisking constantly and vigorously, bring to a boil, then add reserved caramel pieces. Cook, whisking constantly and into the edges of the pot, until mixture is thickened and caramel is melted, about 2 minutes. Remove from heat, whisk for another minute, then let stand 5 minutes. 

Transfer pastry cream to a clean bowl, immediately cover the surface with plastic wrap to prevent a crust from forming and chill until cold, about 1 hour. (Pastry cream can be made up to
1 day ahead.) 

Heat oven to 375° with rack in middle.

FOR PEARS: Cut 1 pear half into 3/4-inch cubes; set aside. In a large skillet, combine sugar and butter. Heat over medium heat until butter is melted and lightly golden, add wine and remaining pear halves, cut-side down. Bring to a simmer and cook until pears are caramelized and liquid is reduced to
about 2 tablespoons, about 20 minutes.

Grease tart pan. On a lightly floured work surface, roll out dough to a 14-inch round. Fit dough into tart pan, pressing into edges. Fold over dough to create double-thick edge. Using a knife, trim excess dough. Transfer caramel cream to tart shell, spreading evenly. Arrange pears on top of cream, cut-side down and with narrow ends facing inwards. Fill spaces between pear halves with cubed pear.

Bake, rotating once halfway through, until fruit is tender and crust is deep golden, about 50 minutes. Transfer pan to wire rack and cool completely, then remove tart from pan. Dust with confectioners sugar just before serving.