Pear Küchen

Stir together milk and 1 teaspoon granulated sugar in bowl of mixer. Sprinkle yeast over mixture and let stand until foamy, about 5 minutes. (If yeast doesn't foam, discard and start over with new yeast.)
Add 1/4 cup flour, beating at medium speed until combined. Add whole egg, yolk, vanilla, salt, and remaining 1/3 cup sugar and beat until combined. Reduce speed to low and gradually mix in 1 1/4 cups remaining flour. Increase speed to medium and add butter, then continue beating, stopping and scraping down side of bowl once or twice, until dough is shiny and forms strands from paddle to bowl, about 3 minutes. (Dough will be very soft and sticky.)
Transfer dough to a lightly oiled bowl and cover with plastic wrap. Let rise in a warm, draft-free place until doubled in bulk, about 1 1/2 hours.
Put oven rack in middle position and preheat oven to 400°F.
Peel pears, cut lengthwise into eighths, and core. Toss pears with melted butter and 2 tablespoons brown sugar in a 13- by 9-inch glass or ceramic baking dish and arrange in 1 layer.
Roast pears, gently turning and stirring occasionally, until just tender and lightly caramelized, about 45 minutes. Transfer pears to a plate with a slotted spatula. Stir bread crumbs into baking dish, scraping up all brown bits and butter, then transfer to a bowl. Stir hazelnuts, cinnamon, and remaining 2 tablespoons brown sugar into bread crumbs.
Reduce oven temperature to 350°F.
Transfer dough to springform pan and spread evenly with a rubber spatula to cover bottom.
Sprinkle half of crumb mixture over dough, leaving a 1-inch border. Gently toss roasted pears with remaining crumb mixture and scatter pears over dough. Let rise, covered with plastic wrap, in a warm draft-free place, 30 minutes.
Bake, uncovered, until firm to the touch and deep golden brown, about 40 minutes. Cool in pan on a rack, 20 minutes, then carefully remove side of pan. Cool to barely warm or room temperature.